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  • 8/9/2019 Machine Learning and Finance II

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    Machine learning and portfolio selections. II.

    Laszlo (Laci) Gyorfi1

    1Department of Computer Science and Information TheoryBudapest University of Technology and Economics

    Budapest, Hungary

    August 8, 2007

    e-mail: [email protected]/gyorfiwww.szit.bme.hu/oti/portfolio

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Dynamic portfolio selection: general case

    xi = (x(1)i , . . . x

    (d)i ) the return vector on day i

    b = b1 is the portfolio vector for the first day

    initial capital S0

    S1 = S0 b1 , x1

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Dynamic portfolio selection: general case

    xi = (x(1)i , . . . x

    (d)i ) the return vector on day i

    b = b1 is the portfolio vector for the first day

    initial capital S0

    S1 = S0 b1 , x1

    for the second day, S1 new initial capital, the portfolio vectorb2 = b(x1)

    S2 = S0 b1 , x1 b(x1) , x2 .

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Dynamic portfolio selection: general case

    xi = (x(1)i , . . . x

    (d)i ) the return vector on day i

    b = b1 is the portfolio vector for the first day

    initial capital S0

    S1 = S0 b1 , x1

    for the second day, S1 new initial capital, the portfolio vectorb2 = b(x1)

    S2 = S0 b1 , x1 b(x1) , x2 .

    nth day a portfolio strategy bn = b(x1, . . . , xn1) = b(xn11 )

    Sn = S0

    n

    i=1b(xi11 ) , xi = S0enWn(B)

    with the average growth rate

    Wn(B) =1

    n

    n

    i=1ln

    b(xi11 ) , xi

    .

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    log-optimum portfolio

    X1, X2, . . . drawn from the vector valued stationary and ergodicprocesslog-optimum portfolio B = {b()}

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } = maxb()

    E{ln

    b(Xn11 ) , Xn

    | Xn11 }

    Xn11 = X1, . . . , Xn1

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Optimality

    Algoet and Cover (1988): If Sn = Sn(B) denotes the capital after

    day n achieved by a log-optimum portfolio strategy B, then for

    any portfolio strategy B with capital Sn = Sn(B) and for anyprocess {Xn}

    ,

    lim supn

    1

    nln Sn

    1

    nln Sn 0 almost surely

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Optimality

    Algoet and Cover (1988): If Sn = Sn(B) denotes the capital after

    day n achieved by a log-optimum portfolio strategy B, then for

    any portfolio strategy B with capital Sn = Sn(B) and for anyprocess {Xn}

    ,

    lim supn

    1

    nln Sn

    1

    nln Sn 0 almost surely

    for stationary ergodic process {Xn},

    limn

    1

    nln Sn = W

    almost surely,

    where

    W = E

    maxb()

    E{ln

    b(X1) , X0

    | X1}

    is the maximal growth rate of any portfolio.

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    Martingale difference sequences

    for the proof of optimality we use the concept of martingale

    differences:

    Definition

    there are two sequences of random variables:

    {Zn} {Xn}

    Zn is a function of X1, . . . , Xn,

    E{Zn | X1, . . . , Xn1} = 0 almost surely.

    Then {Zn} is called martingale difference sequence with respect to{Xn}.

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    A strong law of large numbers

    Chow Theorem: If {Zn} is a martingale difference sequence withrespect to {Xn} and

    n=1

    E{Z2n }

    n2

    <

    then

    limn

    1

    n

    ni=1

    Zi = 0 a.s.

    Gyorfi Machine learning and portfolio selections. II.

    A k l f l b

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Gyorfi Machine learning and portfolio selections. II.

    A k l f l b

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj}

    Gyorfi Machine learning and portfolio selections. II.

    A k l f l b

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    Gyorfi Machine learning and portfolio selections. II.

    A k l f l b

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    Gyorfi Machine learning and portfolio selections. II.

    A k l f l b s

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0}

    Gyorfi Machine learning and portfolio selections. II.

    A weak law of large numbers

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0} = 0

    Gyorfi Machine learning and portfolio selections. II.

    A weak law of large numbers

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0} = 0

    Corollary

    E

    1

    n

    ni=1

    Zi

    2

    Gyorfi Machine learning and portfolio selections. II.

    A weak law of large numbers

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0} = 0

    Corollary

    E

    1

    n

    ni=1

    Zi

    2

    =1

    n2

    ni=1

    nj=1

    E{ZiZj}

    Gyorfi Machine learning and portfolio selections. II.

    A weak law of large numbers

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0} = 0

    Corollary

    E

    1

    n

    ni=1

    Zi

    2

    =1

    n2

    ni=1

    nj=1

    E{ZiZj}

    =1

    n2

    ni=1

    E{Z2i }

    Gyorfi Machine learning and portfolio selections. II.

    A weak law of large numbers

    http://find/http://goback/
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    A weak law of large numbers

    Lemma: If {Zn} is a martingale difference sequence with respectto {Xn} then {Zn} are uncorrelated.

    Proof. Put i < j.E{ZiZj} = E{E{ZiZj | X1, . . . , Xj1}}

    = E{ZiE{Zj | X1, . . . , Xj1}}

    = E{Zi 0} = 0

    Corollary

    E

    1

    n

    ni=1

    Zi

    2

    =1

    n2

    ni=1

    nj=1

    E{ZiZj}

    =1

    n2

    ni=1

    E{Z2i }

    0

    if, for example,E

    {Z2i } is a bounded sequence.

    Gyorfi Machine learning and portfolio selections. II.

    Constructing martingale difference sequence

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    Constructing martingale difference sequence

    {Yn} is an arbitrary sequence such that Yn is a function of

    X1, . . . , Xn

    Gyorfi Machine learning and portfolio selections. II.

    Constructing martingale difference sequence

    http://find/http://goback/
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    Constructing martingale difference sequence

    {Yn} is an arbitrary sequence such that Yn is a function of

    X1, . . . , XnPut

    Zn = Yn E{Yn | X1, . . . , Xn1}

    Then {Zn} is a martingale difference sequence:

    Gyorfi Machine learning and portfolio selections. II.

    Constructing martingale difference sequence

    http://find/http://goback/
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    Constructing martingale difference sequence

    {Yn} is an arbitrary sequence such that Yn is a function of

    X1, . . . , XnPut

    Zn = Yn E{Yn | X1, . . . , Xn1}

    Then {Zn} is a martingale difference sequence:

    Zn is a function of X1, . . . , Xn,

    Gyorfi Machine learning and portfolio selections. II.

    Constructing martingale difference sequence

    http://find/http://goback/
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    Constructing martingale difference sequence

    {Yn} is an arbitrary sequence such that Yn is a function of

    X1, . . . , XnPut

    Zn = Yn E{Yn | X1, . . . , Xn1}

    Then {Zn} is a martingale difference sequence:

    Zn is a function of X1, . . . , Xn,

    E{Zn | X1, . . . , Xn1}

    Gyorfi Machine learning and portfolio selections. II.

    Constructing martingale difference sequence

    http://find/http://goback/
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    C g g q

    {Yn} is an arbitrary sequence such that Yn is a function of

    X1, . . . , XnPut

    Zn = Yn E{Yn | X1, . . . , Xn1}

    Then {Zn} is a martingale difference sequence:

    Zn is a function of X1, . . . , Xn,

    E{Zn | X1, . . . , Xn1}

    = E{Yn E{Yn | X1, . . . , Xn1} | X1, . . . , Xn1}

    = 0

    almost surely.

    Gyorfi Machine learning and portfolio selections. II.

    Optimality

    http://find/http://goback/
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    p y

    log-optimum portfolio B = {b()}

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } = maxb()

    E{ln

    b(Xn11 ) , Xn

    | Xn11 }

    Gyorfi Machine learning and portfolio selections. II.

    Optimality

    http://find/http://goback/
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    p y

    log-optimum portfolio B = {b()}

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } = maxb()

    E{ln

    b(Xn11 ) , Xn

    | Xn11 }

    If Sn = Sn(B) denotes the capital after day n achieved by a

    log-optimum portfolio strategy B, then for any portfolio strategyB with capital Sn = Sn(B) and for any process {Xn}

    ,

    lim supn

    1n ln S

    n 1n ln Sn

    0 almost surely

    Gyorfi Machine learning and portfolio selections. II.

    Proof of optimality

    http://find/http://goback/
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    p y

    1

    n

    ln Sn =1

    n

    n

    i=1

    lnb(Xi11

    ) , Xi

    Gyorfi Machine learning and portfolio selections. II.

    Proof of optimality

    http://find/http://goback/
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    1

    n

    ln Sn =1

    n

    n

    i=1

    lnb(Xi11 ) , Xi=

    1

    n

    ni=1

    E{ln

    b(Xi11 ) , Xi

    | Xi11 }

    +1

    n

    ni=1

    ln

    b(Xi11 ) , Xi

    E{ln

    b(Xi11 ) , Xi

    | Xi11 }

    Gyorfi Machine learning and portfolio selections. II.

    Proof of optimality

    http://find/http://goback/
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    1

    n

    ln Sn =1

    n

    n

    i=1

    lnb(Xi11 ) , Xi=

    1

    n

    ni=1

    E{ln

    b(Xi11 ) , Xi

    | Xi11 }

    +1

    n

    ni=1

    ln

    b(Xi11 ) , Xi

    E{ln

    b(Xi11 ) , Xi

    | Xi11 }

    and

    1

    n ln Sn =

    1

    n

    ni=1

    E{ln

    b

    (Xi11 ) , Xi

    | X

    i11 }

    +1

    n

    ni=1

    ln

    b(Xi11 ) , Xi

    E{ln

    b(Xi11 ) , Xi

    | Xi11 }

    Gyorfi Machine learning and portfolio selections. II.

    Universally consistent portfolio

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    These limit relations give rise to the following definition:

    Definition

    An empirical (data driven) portfolio strategy B is called

    universally consistent with respect to a class C of stationaryand ergodic processes {Xn}

    , if for each process in the class,

    limn

    1

    nln Sn(B) = W

    almost surely.

    Gyorfi Machine learning and portfolio selections. II.

    Empirical portfolio selection

    http://find/http://goback/
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    E{ln b(Xn11 ) , Xn | X

    n11 } = max

    b()E{ln b(X

    n11 ) , Xn | X

    n11 }

    Gyorfi Machine learning and portfolio selections. II.

    Empirical portfolio selection

    http://find/http://goback/
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    E{ln b(Xn11 ) , Xn | X

    n11 } = max

    b()E{ln b(X

    n11 ) , Xn | X

    n11 }

    fixed integer k > 0

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    Gyorfi Machine learning and portfolio selections. II.

    Empirical portfolio selection

    http://find/http://goback/
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    E{ln b(Xn11 ) , Xn | X

    n11 } = max

    b()E{ln b(X

    n11 ) , Xn | X

    n11 }

    fixed integer k > 0

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    and

    b(Xn11 ) bk(Xn1nk) = argmaxb()

    E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    Gyorfi Machine learning and portfolio selections. II.

    Empirical portfolio selection

    http://find/http://goback/
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    E{ln b(Xn11 ) , Xn | X

    n11 } = max

    b()E{ln b(X

    n11 ) , Xn | X

    n11 }

    fixed integer k > 0

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    and

    b(Xn11 ) bk(Xn1nk) = argmaxb()

    E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    because of stationarity

    bk(xk1 ) = argmax

    b()E{lnb(x

    k1 ) , Xk+1 | X

    k1 = x

    k1 }

    = argmaxb

    E{ln b , Xk+1 | Xk1 = x

    k1 },

    Gyorfi Machine learning and portfolio selections. II.

    Empirical portfolio selection

    http://find/http://goback/
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    E{ln b(Xn11 ) , Xn | X

    n11 } = max

    b()E{ln b(X

    n11 ) , Xn | X

    n11 }

    fixed integer k > 0

    E{ln

    b(Xn11 ) , Xn

    | Xn11 } E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    and

    b(Xn11 ) bk(Xn1nk) = argmaxb()

    E{ln

    b(Xn1nk) , Xn

    | Xn1nk}

    because of stationarity

    bk(xk1 ) = argmax

    b()E{lnb(x

    k1 ) , Xk+1 | X

    k1 = x

    k1 }

    = argmaxb

    E{ln b , Xk+1 | Xk1 = x

    k1 },

    which is the maximization of the regression function

    mb(xk1 ) = E{ln b , Xk+1 | X

    k1 = x

    k1 }

    Gyorfi Machine learning and portfolio selections. II.

    Regression function

    http://find/http://goback/
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    Y real valuedX observation vector

    Gyorfi Machine learning and portfolio selections. II.

    Regression function

    http://find/http://goback/
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    Y real valuedX observation vectorRegression function

    m(x) = E{Y | X = x}

    i.i.d. data: Dn = {(X1, Y1), . . . , (Xn, Yn)}

    Gyorfi Machine learning and portfolio selections. II.

    Regression function

    http://find/http://goback/
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    Y real valuedX observation vectorRegression function

    m(x) = E{Y | X = x}

    i.i.d. data: Dn = {(X1, Y1), . . . , (Xn, Yn)}Regression function estimate

    mn(x) = mn(x, Dn)

    Gyorfi Machine learning and portfolio selections. II.

    Regression function

    http://find/http://goback/
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    Y real valuedX observation vectorRegression function

    m(x) = E{Y | X = x}

    i.i.d. data: Dn = {(X1, Y1), . . . , (Xn, Yn)}Regression function estimate

    mn(x) = mn(x, Dn)

    local averaging estimates

    mn(x) =

    ni=1

    Wni(x; X1, . . . , Xn)Yi

    Gyorfi Machine learning and portfolio selections. II.

    Regression function

    http://find/http://goback/
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    Y real valuedX observation vectorRegression function

    m(x) = E{Y | X = x}

    i.i.d. data: Dn = {(X1, Y1), . . . , (Xn, Yn)}Regression function estimate

    mn(x) = mn(x, Dn)

    local averaging estimates

    mn(x) =

    ni=1

    Wni(x; X1, . . . , Xn)Yi

    L. Gyorfi, M. Kohler, A. Krzyzak, H. Walk (2002) ADistribution-Free Theory of Nonparametric Regression,Springer-Verlag, New York.

    Gyorfi Machine learning and portfolio selections. II.

    Correspondence

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    X Xk1

    Gyorfi Machine learning and portfolio selections. II.

    Correspondence

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    X Xk1

    Y ln b , Xk+1

    Gyorfi Machine learning and portfolio selections. II.

    Correspondence

    http://find/http://goback/
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    X Xk1

    Y ln b , Xk+1m(x) = E{Y | X = x} mb(x

    k1 ) = E{ln b , Xk+1 | X

    k1 = x

    k1 }

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning regression estimate

    http://find/http://goback/
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    Partition Pn = {An,1, An,2 . . . }

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning regression estimate

    http://find/http://goback/
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    Partition Pn = {An,1, An,2 . . . }An(x) is the cell of the partition Pn into which x falls

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning regression estimate

    http://find/http://goback/
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    Partition Pn = {An,1, An,2 . . . }An(x) is the cell of the partition Pn into which x falls

    mn(x) =

    ni=1 YiI[XiAn(x)]ni=1 I[XiAn(x)]

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning regression estimate

    http://find/http://goback/
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    Partition Pn = {An,1, An,2 . . . }An(x) is the cell of the partition Pn into which x falls

    mn(x) =

    ni=1 YiI[XiAn(x)]ni=1 I[XiAn(x)]

    Let Gn be the quantizer corresponding to the partition Pn:Gn(x) = j if x An,j.

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning regression estimate

    http://find/http://goback/
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    Partition Pn = {An,1, An,2 . . . }An(x) is the cell of the partition Pn into which x falls

    mn(x) =

    ni=1 YiI[XiAn(x)]ni=1 I[XiAn(x)]

    Let Gn be the quantizer corresponding to the partition Pn:Gn(x) = j if x An,j.the set of matches

    In = {i n : Gn(x) = Gn(Xi)}

    Then

    mn(x) =

    iIn

    Yi

    |In|.

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning-based portfolio selection

    http://find/http://goback/
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    fix k, = 1, 2, . . .P = {A,j,j = 1, 2, . . . , m} finite partitions ofRd,

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning-based portfolio selection

    http://find/http://goback/
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    fix k, = 1, 2, . . .P = {A,j,j = 1, 2, . . . , m} finite partitions ofRd,G be the corresponding quantizer: G(x) = j, if x A,j.

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning-based portfolio selection

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    fix k, = 1, 2, . . .

    P = {A,j,j = 1, 2, . . . , m} finite partitions ofRd,G be the corresponding quantizer: G(x) = j, if x A,j.G(x

    n1) = G(x1), . . . , G(xn),

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning-based portfolio selection

    http://find/http://goback/
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    fix k, = 1, 2, . . .

    P = {A,j,j = 1, 2, . . . , m} finite partitions ofRd,G be the corresponding quantizer: G(x) = j, if x A,j.G(x

    n1) = G(x1), . . . , G(xn),

    the set of matches:

    Jn = {k < i < n : G(xi1ik) = G(xn1nk)}

    Gyorfi Machine learning and portfolio selections. II.

    Partitioning-based portfolio selection

    http://find/http://goback/
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    fix k, = 1, 2, . . .

    P = {A,j,j = 1, 2, . . . , m} finite partitions ofRd,G be the corresponding quantizer: G(x) = j, if x A,j.G(x

    n1) = G(x1), . . . , G(xn),

    the set of matches:

    Jn = {k < i < n : G(xi1ik) = G(xn1nk)}

    b(k,)(xn11 ) = argmaxb iJn

    ln b , xi

    if the set In is non-void, and b0 = (1/d, . . . , 1/d) otherwise.

    Gyorfi Machine learning and portfolio selections. II.

    Elementary portfolios

    http://find/http://goback/
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    for fixed k, = 1, 2, . . .,B(k,) = {b(k,)()}, are called elementary portfolios

    Gyorfi Machine learning and portfolio selections. II.

    Elementary portfolios

    http://find/http://goback/
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    for fixed k, = 1, 2, . . .,B(k,) = {b(k,)()}, are called elementary portfolios

    That is, b(k,)n quantizes the sequence x

    n11 according to the

    partition P, and browses through all past appearances of the lastseen quantized string G(x

    n1nk) of length k.

    Then it designs a fixed portfolio vector according to the returns onthe days following the occurence of the string.

    Gyorfi Machine learning and portfolio selections. II.

    Combining elementary portfolios

    http://find/http://goback/
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    How to choose k,

    small k or small : large bias

    large k and large : few matching, large variance

    Gyorfi Machine learning and portfolio selections. II.

    Combining elementary portfolios

    http://find/http://goback/
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    How to choose k,

    small k or small : large bias

    large k and large : few matching, large variance

    Machine learning: combination of experts

    N. Cesa-Bianchi and G. Lugosi, Prediction, Learning, and Games.Cambridge University Press, 2006.

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighing

    combine the elementary portfolio strategies B(k,) = {b(k,)n }

    http://find/http://goback/
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    y p g { n }

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighing

    combine the elementary portfolio strategies B(k,) = {b(k,)n }

    http://find/http://goback/
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    y p g { n }let {qk,} be a probability distribution on the set of all pairs (k, )such that for all k, , qk, > 0.

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighing

    combine the elementary portfolio strategies B(k,) = {b(k,)n }

    http://find/http://goback/
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    y p g { }let {qk,} be a probability distribution on the set of all pairs (k, )such that for all k, , qk, > 0.

    for > 0 putwn,k, = qk,e

    lnSn1(B(k,))

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighing

    combine the elementary portfolio strategies B(k,) = {b(k,)n }

    http://find/http://goback/
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    g { }let {qk,} be a probability distribution on the set of all pairs (k, )such that for all k, , qk, > 0.

    for > 0 putwn,k, = qk,e

    lnSn1(B(k,))

    for = 1,

    wn,k, = qk,elnSn

    1(B(k,)

    ) = qk,Sn1(B(k,

    ))

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighingcombine the elementary portfolio strategies B(k,) = {b

    (k,)n }

    http://find/http://goback/
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    let {qk,} be a probability distribution on the set of all pairs (k, )such that for all k, , qk, > 0.

    for > 0 putwn,k, = qk,e

    lnSn1(B(k,))

    for = 1,

    wn,k, = qk,elnSn

    1(B(k,)

    ) = qk,Sn1(B(k,

    ))

    andvn,k, =

    wn,k,

    i,jwn,i,j

    .

    Gyorfi Machine learning and portfolio selections. II.

    Exponential weighingcombine the elementary portfolio strategies B(k,) = {b

    (k,)n }

    http://find/http://goback/
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    let {qk,} be a probability distribution on the set of all pairs (k, )such that for all k, , qk, > 0.

    for > 0 putwn,k, = qk,e

    lnSn1(B(k,))

    for = 1,

    wn,k, = qk,elnS

    n

    1(B(k,))

    = qk,Sn1(B(k,)

    )

    andvn,k, =

    wn,k,

    i,jwn,i,j

    .

    the combined portfolio b:

    bn(xn11 ) =

    k,

    vn,k,b(k,)n (x

    n11 ).

    Gyorfi Machine learning and portfolio selections. II.

    n

    http://find/http://goback/
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    Sn(B) =n

    i=1bi(x

    i11 ) , xi

    Gyorfi Machine learning and portfolio selections. II.

    n

    http://find/http://goback/
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    Sn(B) =n

    i=1bi(x

    i11 ) , xi

    =n

    i=1

    k, wi,k,

    b

    (k,)i (x

    i11 ) , xi

    k, wi,k,

    Gyorfi Machine learning and portfolio selections. II.

    n

    http://find/http://goback/
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    Sn(B) =n

    i=1bi(x

    i11 ) , xi

    =n

    i=1

    k, wi,k,

    b

    (k,)i (x

    i11 ) , xi

    k, wi,k,

    =

    ni=1

    k, qk,Si1(B(k,))b(k,)i (xi11 ) , xik, qk,Si1(B

    (k,))

    Gyorfi Machine learning and portfolio selections. II.

    n

    http://find/http://goback/
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    Sn(B) =n

    i=1bi(x

    i11 ) , xi

    =n

    i=1

    k, wi,k,

    b

    (k,)i (x

    i11 ) , xi

    k, wi,k,

    =

    ni=1

    k, qk,Si1(B(k,))b(k,)i (xi11 ) , xik, qk,Si1(B

    (k,))

    =n

    i=1

    k, qk,Si(B(k,))

    k, qk,Si1(B(k,))

    Gyorfi Machine learning and portfolio selections. II.

    n

    http://find/http://goback/
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    Sn(B) =n

    i=1bi(x

    i11 ) , xi

    =n

    i=1

    k, wi,k,

    b

    (k,)i (x

    i11 ) , xi

    k, wi,k,

    =

    ni=1

    k, qk,Si1(B(k,))b(k,)i (xi11 ) , xik, qk,Si1(B

    (k,))

    =n

    i=1

    k, qk,Si(B(k,))

    k, qk,Si1(B(k,))

    =k,

    qk,Sn(B(k,)),

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    The strategy B = BH then arises from weighing the elementary

    portfolio strategies B(k,) = {b(k,)n } such that the investors capital

    becomesSn(B) =

    k,

    qk,Sn(B(k,)).

    Gyorfi Machine learning and portfolio selections. II.

    Theorem

    http://find/http://goback/
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    Assume that

    (a) the sequence of partitions is nested, that is, any cell of P+1 isa subset of a cell of P, = 1, 2, . . .;

    (b) ifdiam(A) = supx,yA x y denotes the diameter of a set,then for any sphere S centered at the origin

    lim

    maxj:A,jS=

    diam(A,j) = 0 .

    Then the portfolio scheme BH defined above is universallyconsistent with respect to the class of all ergodic processes suchthat E{| ln X(j)| < , for j = 1, 2, . . . , d.

    Gyorfi Machine learning and portfolio selections. II.

    http://find/http://goback/
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    L. Gyorfi, D. Schafer (2003) Nonparametric prediction, inAdvances in Learning Theory: Methods, Models and Applications,J. A. K. Suykens, G. Horvath, S. Basu, C. Micchelli, J. Vandevalle(Eds.), IOS Press, NATO Science Series, pp. 341-356.

    www.szit.bme.hu/gyorfi/histog.ps

    Gyorfi Machine learning and portfolio selections. II.

    ProofWe have to prove that

    1

    http://find/http://goback/
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    lim infn

    Wn(B) = lim infn

    1

    nln Sn(B) W

    a.s.

    W.l.o.g. we may assume S0 = 1, so that

    Wn(B) =1

    nln Sn(B)

    Gyorfi Machine learning and portfolio selections. II.

    ProofWe have to prove that

    1

    http://find/http://goback/
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    lim infn

    Wn(B) = lim infn

    1

    nln Sn(B) W

    a.s.

    W.l.o.g. we may assume S0 = 1, so that

    Wn(B) =1

    nln Sn(B)

    =

    1

    n ln

    k,qk,Sn(B

    (k,)

    )

    Gyorfi Machine learning and portfolio selections. II.

    ProofWe have to prove that

    1

    http://find/http://goback/
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    lim infn

    Wn(B) = lim infn

    1

    nln Sn(B) W

    a.s.

    W.l.o.g. we may assume S0 = 1, so that

    Wn(B) =1

    nln Sn(B)

    =

    1

    n ln

    k,qk,Sn(B

    (k,)

    )

    1

    nln

    supk,

    qk,Sn(B(k,))

    Gyorfi Machine learning and portfolio selections. II.

    ProofWe have to prove that

    1

    http://find/http://goback/
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    lim infn

    Wn(B) = lim infn

    1

    nln Sn(B) W

    a.s.

    W.l.o.g. we may assume S0 = 1, so that

    Wn(B) =1

    nln Sn(B)

    =

    1

    n ln

    k,qk,Sn(B

    (k,)

    )

    1

    nln

    supk,

    qk,Sn(B(k,))

    = 1n

    supk,

    ln qk, + ln Sn(B(k,))

    Gyorfi Machine learning and portfolio selections. II.

    ProofWe have to prove that

    1

    http://find/http://goback/
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    lim infn

    Wn(B) = lim infn

    1

    nln Sn(B) W

    a.s.

    W.l.o.g. we may assume S0 = 1, so that

    Wn(B) =1

    nln Sn(B)

    =

    1

    n ln

    k,qk,Sn(B

    (k,)

    )

    1

    nln

    supk,

    qk,Sn(B(k,))

    = 1n

    supk,

    ln qk, + ln Sn(B(k,))

    = sup

    k,

    Wn(B

    (k,)) +ln qk,

    n

    .

    Gyorfi Machine learning and portfolio selections. II.

    Thus

    l

    http://find/http://goback/
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    lim infn

    Wn(B) lim infn

    sup

    k,Wn(B(k,)) +

    ln qk,n

    Gyorfi Machine learning and portfolio selections. II.

    Thus

    l

    http://find/http://goback/
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    lim infn

    Wn(B) lim infn

    sup

    k,Wn(B(k,)) +

    ln qk,n

    supk,

    lim infn

    Wn(B

    (k,)) +ln qk,

    n

    Gyorfi Machine learning and portfolio selections. II.

    Thus

    ln q

    http://find/http://goback/
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    lim infn

    Wn(B) lim infn

    sup

    k,Wn(B(k,)) +

    ln qk,n

    supk,

    lim infn

    Wn(B

    (k,)) +ln qk,

    n

    = supk,

    lim infn

    Wn(B(k,))

    Gyorfi Machine learning and portfolio selections. II.

    Thus

    ln q

    http://find/http://goback/
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    lim infn

    Wn(B) lim infn

    supk,Wn(B(k,)) +

    ln qk,n

    supk,

    lim infn

    Wn(B

    (k,)) +ln qk,

    n

    = supk,

    lim infn

    Wn(B(k,))

    = supk,

    k,

    Since the partitions P are nested, we have that

    supk,

    k,

    = limk

    liml

    k,

    = W.

    Gyorfi Machine learning and portfolio selections. II.

    Kernel regression estimate

    http://find/http://goback/
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    Kernel function K(x) 0Bandwidth h > 0

    mn(x) =

    ni=1 YiK

    xXih

    ni

    =1

    K xXih

    Naive (window) kernel function K(x) = I{x1}

    mn(x) = ni=1 YiI{xXih}

    ni=1 I{xXih}

    Gyorfi Machine learning and portfolio selections. II.

    Kernel-based portfolio selection

    http://find/http://goback/
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    choose the radius rk, > 0 such that for any fixed k,

    lim

    rk, = 0.

    Gyorfi Machine learning and portfolio selections. II.

    Kernel-based portfolio selection

    http://find/http://goback/
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    choose the radius rk, > 0 such that for any fixed k,

    lim

    rk, = 0.

    for n > k + 1, define the expert b(k,) by

    b(k,)(xn11 ) = argmaxb

    {k

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    The kernel-based portfolio scheme is universally consistent withrespect to the class of all ergodic processes such thatE{| ln X(j)| < , for j = 1, 2, . . . , d.

    L. Gyorfi, G. Lugosi, F. Udina (2006) Nonparametric kernel-basedsequential investment strategies, Mathematical Finance, 16, pp.337-357www.szit.bme.hu/gyorfi/kernel.pdf

    Gyorfi Machine learning and portfolio selections. II.

    k-nearest neighbor (NN) regression estimate

    http://find/http://goback/
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    mn(x) =n

    i=1Wni(x; X1, . . . , Xn)Yi.

    Wni is 1/k if Xi is one of the k nearest neighbors of x amongX1, . . . , Xn, and Wni is 0 otherwise.

    Gyorfi Machine learning and portfolio selections. II.

    Nearest-neighbor-based portfolio selection

    choose p (0 1) such that lim p = 0

    http://find/http://goback/
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    choose p (0, 1) such that lim p 0for fixed positive integers k, (n > k + + 1) introduce the set ofthe = pn nearest neighbor matches:

    J(k,)n = {i; k + 1 i n such that x

    i1ik is among the NNs of x

    n1nk

    in xk1 , . . . , xn1nk}.

    Gyorfi Machine learning and portfolio selections. II.

    Nearest-neighbor-based portfolio selection

    choose p (0, 1) such that lim p = 0

    http://find/http://goback/
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    choose p (0, 1) such that lim p 0for fixed positive integers k, (n > k + + 1) introduce the set ofthe = pn nearest neighbor matches:

    J(k,)n = {i; k + 1 i n such that x

    i1ik is among the NNs of x

    n1nk

    in xk1 , . . . , xn1nk}.

    Define the portfolio vector by

    b(k,)(xn11 ) = argmaxb

    iJ

    (k,)n

    ln b , xi

    if the sum is non-void, and b0 = (1/d, . . . , 1/d) otherwise.

    Gyorfi Machine learning and portfolio selections II

    Theorem

    If for any vector s = sk1 the random variable

    http://find/http://goback/
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    y 1

    Xk1 s

    has continuous distribution function, then the nearest-neighborportfolio scheme is universally consistent with respect to the classof all ergodic processes such that E{| ln X(j)|} < , for

    j = 1, 2, . . . d.

    NN is robust, there is no scaling problem

    Gyorfi Machine learning and portfolio selections II

    Theorem

    If for any vector s = sk1 the random variable

    http://find/http://goback/
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    y 1

    Xk1 s

    has continuous distribution function, then the nearest-neighborportfolio scheme is universally consistent with respect to the classof all ergodic processes such that E{| ln X(j)|} < , for

    j = 1, 2, . . . d.

    NN is robust, there is no scaling problem

    L. Gyorfi, F. Udina, H. Walk (2006) Nonparametric nearest

    neighbor based empirical portfolio selection strategies,(submitted), www.szit.bme.hu/gyorfi/NN.pdf

    Gyorfi Machine learning and portfolio selections II

    Semi-log-optimal portfolio

    empirical log-optimal:

    (k ) 1

    http://find/http://goback/
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    h(k,)(xn11 ) = argmax

    biJn

    ln b , xi

    Gyorfi Machine learning and portfolio selections II

    Semi-log-optimal portfolio

    empirical log-optimal:

    (k ) 1

    http://find/http://goback/
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    h(k,)(xn11 ) = argmax

    biJn

    ln b , xi

    Taylor expansion: ln z h(z) = z 1 12 (z 1)2

    Gyorfi Machine learning and portfolio selections II

    Semi-log-optimal portfolio

    empirical log-optimal:

    (k )( n 1)

    http://find/http://goback/
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    h(k,)(xn11 ) = argmax

    biJn

    ln b , xi

    Taylor expansion: ln z h(z) = z 1 12 (z 1)2 empirical

    semi-log-optimal:

    h(k,)(xn11 ) = argmaxb

    iJn

    h(b , xi) = argmaxb

    {b , mb , Cb}

    Gyorfi Machine learning and portfolio selections II

    Semi-log-optimal portfolio

    empirical log-optimal:

    h(k )( n 1) l b

    http://find/http://goback/
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    h(k,)(xn11 ) = argmax

    biJn

    ln b , xi

    Taylor expansion: ln z h(z) = z 1 12 (z 1)2 empirical

    semi-log-optimal:

    h(k,)(xn11 ) = argmaxb

    iJn

    h(b , xi) = argmaxb

    {b , mb , Cb}

    smaller computational complexity: quadratic programming

    Gyorfi Machine learning and portfolio selections II

    http://find/http://goback/
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    Conditions of the model:

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    Assume that

    the assets are arbitrarily divisible,

    the assets are available in unbounded quantities at the currentprice at any given trading period,

    there are no transaction costs,

    the behavior of the market is not affected by the actions ofthe investor using the strategy under investigation.

    Gyorfi Machine learning and portfolio selections II

    NYSE data sets

    http://find/http://goback/
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    At www.szit.bme.hu/~oti/portfolio there are two benchmarkdata set from NYSE:

    The first data set consists of daily data of 36 stocks withlength 22 years.

    The second data set contains 23 stocks and has length 44years.

    Gyorfi Machine learning and portfolio selections II

    NYSEdata sets

    http://find/http://goback/
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    At www.szit.bme.hu/~oti/portfolio there are two benchmarkdata set from NYSE:

    The first data set consists of daily data of 36 stocks withlength 22 years.

    The second data set contains 23 stocks and has length 44years.

    Our experiment is on the second data set.

    Gyorfi Machine learning and portfolio selections II

    Experiments on average annual yields (AAY)

    http://find/http://goback/
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    Kernel based semi-log-optimal portfolio selection withk = 1, . . . , 5 and l = 1, . . . , 10

    r2k,l = 0.0001 d k ,

    Gyorfi Machine learning and portfolio selections. II.

    Experiments on average annual yields (AAY)

    http://find/http://goback/
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    Kernel based semi-log-optimal portfolio selection withk = 1, . . . , 5 and l = 1, . . . , 10

    r2k,l = 0.0001 d k ,

    AAY of kernel based semi-log-optimal portfolio is 222.7%

    Gyorfi Machine learning and portfolio selections. II.

    Experiments on average annual yields (AAY)

    http://find/http://goback/
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    Kernel based semi-log-optimal portfolio selection withk = 1, . . . , 5 and l = 1, . . . , 10

    r2k,l = 0.0001 d k ,

    AAY of kernel based semi-log-optimal portfolio is 222.7%double the capital

    Gyorfi Machine learning and portfolio selections. II.

    Experiments on average annual yields (AAY)

    http://find/http://goback/
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    Kernel based semi-log-optimal portfolio selection withk = 1, . . . , 5 and l = 1, . . . , 10

    r2k,l = 0.0001 d k ,

    AAY of kernel based semi-log-optimal portfolio is 222.7%double the capitalMORRIS had the best AAY, 30.1%

    Gyorfi Machine learning and portfolio selections. II.

    Experiments on average annual yields (AAY)

    http://find/http://goback/
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    Kernel based semi-log-optimal portfolio selection withk = 1, . . . , 5 and l = 1, . . . , 10

    r2k,l = 0.0001 d k ,

    AAY of kernel based semi-log-optimal portfolio is 222.7%double the capitalMORRIS had the best AAY, 30.1%the BCRP had average AAY 35.2%

    Gyorfi Machine learning and portfolio selections. II.

    The average annual yields of the individual experts.

    k 1 2 3 4 5

    http://find/http://goback/
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    1 29.4% 27.8% 22.9% 23.9% 23.7%

    2 201.0% 124.6% 98.3% 36.1% 90.8%

    3 114.2% 62.9% 38.8% 91.4% 31.6%

    4 172.5% 155.0% 100.6% 162.3% 50.8%

    5 233.5% 170.2% 166.6% 171.1% 107.7%6 245.4% 216.2% 176.9% 182.0% 143.0%

    7 261.8% 211.0% 181.2% 165.6% 158.7%

    8 229.4% 189.2% 171.0% 138.8% 131.3%

    9 219.3% 172.8% 162.4% 118.7% 116.0%

    10 210.6% 151.5% 131.8% 103.4% 110.9%

    Gyorfi Machine learning and portfolio selections. II.

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