Computer Applications LabComputer Applications LabLab 4Lab 4

Functions and Script Files Functions and Script Files

Chapter 3Chapter 3Chapter 3Chapter 3Sections 1,2,3,4Sections 1,2,3,4

Dr. Iyad Jafar

Adapted from the publisher slides

OutlineOutline

� Passing function arguments

� Common mathematical functions in Matlab

� Script files� Script files

� User-defined functions

� Importing and Exporting Data

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Passing Function ArgumentsPassing Function Arguments

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Passing Function ArgumentsPassing Function Arguments

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Common Mathematical Common Mathematical FunctionsFunctions

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Common Mathematical Common Mathematical FunctionsFunctions

>> x = 3 + 4j

>> abs(x)

ans = 5

>> angle(x)

ans = 53.1301

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>> conj(x)

ans = 3 -4j

>> imag(x)

ans = 4

>> real(x)

ans = 3

Common Mathematical Common Mathematical FunctionsFunctions

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>> x = [5,7,15] ; >> y = sqrt(x) ; y =

2.2361 2.6358 3.8730 >> ceil(y) ans = 3,3,4>> fix(y) ans = 2,2,3

>> floor(y) ans = 2,2,3>> round(y) ans = 2,3,4>> sign(y) Ans = 1 1 1

Common Mathematical Common Mathematical FunctionsFunctions

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Common Mathematical Common Mathematical FunctionsFunctions

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Common Mathematical Common Mathematical FunctionsFunctions

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Script Files Script Files -- IntroductionIntroduction

� Up to this point, we have used Matlab in the interactive mode (commands are entered in the Command window) .

� The interactive mode is desirable when we have few commands.few commands.

� For larger problems we usually use a Script file.

� Basically, the script file contains the same Matlab commands that we type on the command prompt (we don’t have to retype everything if we want to execute/change the commands again.

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Script Files Script Files -- CreationCreation

� Use the Matlab editor/debugger to create your script file. Available from File>New>M-file or by clicking the new M-file shortcut .

� Enter your commands as desired

� Use

◦ ‘;’ to suppress the result of commands

◦ ‘%’ to insert comments; inline or full-line comments

� Script files are saved in Matlab with .m extension.

� Run your script file by typing fileName.m on the command prompt or click on the run shortcut in the editor .

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Script Files Script Files -- ExampleExample

Problem

� The speed v of a falling object dropped with no initial velocity is given as a function of time t by v= gt.velocity is given as a function of time t by v= gt.

� Plot v as a function of t for 0 ≤ t≤ tf, where tf is the final time entered by the user.

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Script Files Script Files -- ExampleExample

% Comments section

% Program falling speed.m:

% Plots speed of a falling object.

% Created on March 1, 2004 by W. Palm

%

% Input Variable:% Input Variable:

% tf= final time (in seconds)

%

% Output Variables:

% t = array of times at which speed is

% computed (in seconds)

% v = array of speeds (meters/second)

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Script Files Script Files -- ExampleExample

% Parameter Value:

g = 9.81;

% Acceleration in SI units

% Input section:

tf = input(’Enter final time in seconds:’);

% Calculation section:% Calculation section:

dt= tf/500;

% Create an array of 501 time values.

t = [0:dt:tf];

% Compute speed values.

v = g*t;

% Output section:

Plot(t,v),xlabel(’t(s)’),ylabel(’vm/s)’)

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Notes on Script File NamesNotes on Script File Names

1. The name of a script file must begin with a letter, and may include digits and the underscore character, up to 31 characters.

2. Do not give a script file the same name as a 2. Do not give a script file the same name as a variable.

3. Do not give a script file the same name as a Matlab command or function. You can check to see if a command, function or file name already exists by using the exist command.

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Some Input/output CommandsSome Input/output Commands

Command Description

disp(A) Displays the contents, but not the name, of the array A.

disp(’text’) Displays the text string enclosed within quotes.

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quotes.

x = input(’text’)

Displays the text in quotes, waits for user input from the keyboard, and stores the value in x.

x = input(’text’,’s’)

Displays the text in quotes, waits for user input from the keyboard, and stores the input as a string in x.

UserUser--defined Functionsdefined Functions

� Another type of m-files.

� It is simply a script file that implements some operation that is not available in Matlab.

� It uses Matlab commands and accepts user arguments.

� To define your function, begin the script file with

function [output variables] = name(input variables)function [output variables] = name(input variables)

� Note:

◦ the output variables are enclosed in square brackets.

◦ the input variables must be enclosed with parentheses.

◦ The function name should be the same as the file name in which it is saved (with the .m extension).

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UserUser--defined Functions defined Functions -- ExampleExample� Example

function z = fun(x,y)

u = 3*x;

z = u + 6*y.^2;

� Call this function with its output argument:

>> z = fun(3,7)

z = 303z = 303

� The function uses x = 3 and y = 7 to compute z.

Note

• the use of a semicolon at the end of the lines prevents the values of u and z from being displayed.

• the use of the array exponentiation operator (.^). This enables the function to accept y as an array.

• the variables defined inside the function are local to the function and are cleared when the function returns 19

Example of Function Definition Example of Function Definition LinesLines

1. One input, one output: function names in red letters

function [area_square] = square(side) square.m

2. Brackets are optional for one input, one output:

function area_square = square(side) square.mfunction area_square = square(side) square.m

3. Three inputs, one output:

function [volume_box] = box(height,width,length) box.m

4. One input, two outputs:

function [area_circle,circumf] = circle(radius) circle.m

5. No named output:

function sqplot(side) sqplot.m

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FunctionsFunctions-- Local VariablesLocal Variables

� The names of the input variables given in the function definition line are local to that function.

� This means that other variable names can be � This means that other variable names can be used when you call the function.

� All variables inside a function are erased after the function finishes executing, except when the same variable names appear in the output variable list used in the function call.

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Functions Functions –– Global VariablesGlobal Variables

� The global keyword declares certain variables global, and therefore their values are available to the basic workspace and to other functions that declare these variables global. declare these variables global.

� The syntax to declare the variables a, x, and q is global a x q

� Any assignment to those variables, in any function or in the base workspace, is available to all the other functions declaring them global.

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SubfunctionsSubfunctions

� Primary : the first function in an m-file and has the same name as the file name. used to call the function from the command line or from other m-file.

� Subfunctions : functions defined in the same file as the primary function and they are available to it only (except with function handles). Used to break large tasks into smaller oners

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SubfunctionsSubfunctions -- ExampleExample

% function to compute circle parameters

% Inputs: radius of the circle

% outputs:

% 1) area: area of circle

% 2) cricum: circumference of the circle% 2) cricum: circumference of the circle

% the function contains two subfunctions; computeArea and

% computeCircum to calculate the area and the circumference

% the given radius

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% main function

function [area,circum] = circleParameters(radius)

area = computeArea(radius) ;

circum = computeCircum(radius) ;

% function to compute the area

function a = computeArea(r)

SubfunctionsSubfunctions –– Example Cont’dExample Cont’d

function a = computeArea(r)

a = pi*r^2;

% function to compute circumference

function c = computeCircum(r)

c = 2*pi*r;

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Functions Handle @Functions Handle @

� It is used to call functions indirectly.

� The handle then can be used as an argument to other functions or as a new function that accepts argumentsfunction that accepts arguments

� For Matlab functions

fHanldle = @functionName

� For anonymous functions

fHandle = @ (argList) anonymus function

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Functions Handle @Functions Handle @

� Example 1 : creating handle for a Matlab function>> fhandle = @humps;>> x = fminbnd(fhandle, 0.3, 1)x =

0.6370

� Example 2: creating and using a handle to anonymous function� Example 2: creating and using a handle to anonymous function>> sqr = @(x) x.^2;>> a = sqr(5)a =

25>> quad(sqr, 0, 1)ans =

0.3333

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fzerofzero functionfunction

� Use fzero function to find the zero(s) of a function of single variable, denoted by x.

fzero(‘function’,x0)

� function is the function expression as a string.

� x0 is the initial guess of the solution.� x0 is the initial guess of the solution.

� For example, fzero(’cos’,2) returns the value 1.5708.

� The function fzero(‘function’,x0) tries to find a zero of function near x0, if x0 is a scalar. fzero(‘function’,[x1 x2] searches for the zero in the interval [x1,x2]. The value returned by fzero is near a point where function changes sign or NaN if the search fails.

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fminbndfminbnd functionfunction

� The fminbnd function finds the minimum of a function of a single variable, which is denoted by x.

� One form of its syntax is fminbnd (’function’, x1, x2) fminbnd (’function’, x1, x2)

where function is a string containing the expression to be minimized.

� The fminbnd function returns a value of x that minimizes the function in the interval x1 ≤x ≤x2. For example, fminbnd(’cos’,0,4) returns the value 3.1416.

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fminsearchfminsearch FunctionFunction

� The fminsearch function finds the minimum of a function of several variables, which is denoted by x.

� One form of its syntax is fminsearch(function, x0)

where function is a function handle for the function where function is a function handle for the function to be minimized and x0 is a vector for initial point.

� Example - find the minimum of f(x,y) = x*exp(-x2 –y2)

>> % define the function handle

>> f = @ (x) x(1)*exp(-(x(1))^2 – (x(2))^2)

>> fminsearch(f,[0,0])

ans = -0.7071 0.000

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Working with Data FilesWorking with Data Files

� Matlab has the capability of importing data created by other application into its workspace.

� Also, it is capable of exporting workspace � Also, it is capable of exporting workspace variables so that it can be used by other applications

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Importing & Exporting Importing & Exporting Spreadsheet FilesSpreadsheet Files

� The command

A = xlsread(’filename’)

imports the Microsoft Excel workbook file filename.xls into the array A.

� The command � The command

[A, B] = xlsread(’filename’)

imports all numeric data into the array A and all text data into the cell arrayB

� The command

[SUCCESS,MESSAGE]=xlswrite(FILE,ARRAY)

writes the ARRAY into and xls file whose name is given by FILE.

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Spreadsheet ExamplesSpreadsheet Examples>> [num,charc] =

xlsread(‘e1.xls’)

num =

1.3000 2.1000 29.0000

3.5000 9.0300 3.1000

0.1000 2.0330 2.1000

-2.0000 -0.2000 0.3000

22.0000 1.0000 0.5552

14.0000 - 123.0000 7.0000

Exa

mp

le 1

14.0000 - 123.0000 7.0000

charc =

'x' 'y' 'z'

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e1.xls

>> a = [2 , 3 ; 4 , 5] ;

>> [succes,message] = xlswrite(‘e2.xls’,a)

succes =

1

message =

message: ''

identifier: ''

Exa

mp

le 2

Working with CSV filesWorking with CSV files

� CSV stands for Comma-Separated Values

� One format that is used to exchange data between applications

� Some properties � Some properties ◦ Each record is a line

◦ Records are separated by a carriage return and a line feed pair.

◦ Record fields are separated by commas.

◦ leading and trailing spaces adjacent to commas are ignored.

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Working with CSV filesWorking with CSV files

� Commands to

◦ Read CSV data into matrix X

X = csvread (fileName)

◦Write matrix M into file fileName◦Write matrix M into file fileName

csvwrite(fileName,M)

>> x = csvread('csvExample.csv')

x =

1 3 10 20

-9 2 1 12

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Working with ASCII FilesWorking with ASCII Files

� Many applications support the ASCII file format.

� If the ASCII file contains a header or the data is separated by commas , you have to remove the header and replace the commas with spaces (one at least); otherwise Matlab will produce an error message.

� To load the data in filename into matrix S

S = load(‘filename’)

� To save ASCII data

save filename A - ASCII

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