w8 matlab programming (edited)

7/27/2019 w8 MATLAB Programming (Edited)

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Introduction to MATLAB

Programming


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Programming - 2Introduction to MATLAB

Programs are contained in m-files

- Plain files not binary files produced by word- Files must have an .m extension m-files must be in path When you call an M-file function from either the command line

or

from within another M-file, MATLAB parses the function andstores it

in memory.

This prevents MATLAB from having to reparse a function eachtime you call it during a session.

The compiled function remains in memory until you clear itusing the

CLEAR command, or until you quit MATLAB.


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TWO TYPES OF M-FILES

1. Scripts-Automate long sequences of commands

2. Functions

- provide extensibility to MATLAB. They allow you to add newfunctions to the existing functions


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Script M-files

- Standard ASCII text files- Contains series of MATLAB expressions stored together in apredefined sequence.

- Saved with an .m extension and are called by simply typingthe filename without the extension in the command window.

Downside of u sing Scr ip t f iles:

- All variables created are added to the workspace.

- Variables already existing in the workspace may be overwritten


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Functions M-files

- Functions are subprograms- Use input and output parameters to communicate with otherfunction

Differences between Scr ipt & Funct ion M-f i les:

Structural Syntax - must contain keyword FUNCTION at thebeginning of the first line

Function Workspaces, Inputs & Outputs- A function does not work with variables in the base MATLAB

workspace.

As a result, all information to be transferred between theMATLAB workspace and a function must bepassedas inputs &outputs.


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function y = mean(x)

% MEAN Average or mean value.

% For vectors, MEAN(x) returns the mean value.

% For matrices, MEAN(x) is a row vector

% containing the mean value of each column.

[m,n] = size(x);

if m == 1m = n;

end

y = sum(x)/m;

Structure of a Function M-file

Keyword: function Function Name (same as file name .m)

Output Argument(s) Input Argument(s)

Online Help

MATLAB

Code

output_value = mean(input_value) Command Line Syntax


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Inputs to Functions : input function can be used to prompt the user for numeric or

string input

Input parameters to functions are preferred

Text output from functions:

dispfunction for simple output

fprintffunction for formatted output.

Text Input and Output


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Prompting for User Input

The input function can be used to prompt the user for numericor string input.

Syntax: entry = input (Text Display)

entry = input (Text Display, s )

Examples:

>> x = input (Enter a value for x)

Enter a value for x %serves as a prompt on the screen thatsignifies that MATLAB is awaiting for user

response.

>>yourName = input (Enter your name,s); %like the previouscommand but will return the entered string as atext variable rather than as a variable name ornumerical value.


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Text Output with disp

- Output to the command window is achieved with the dispfunction

disp Simple to use. Provides limited control over appearance ofoutput.

Syntax: disp (variable)

disp (text string)

Examples:

>>poly_roots = [ 1.2400 2.5600 5.6400 ]

>> disp ('The roots of the cubic polynomial are')

The roots of the cubic polynomial are

>> disp (poly_roots)

1.2400 2.5600 5.6400

>> disp ('The roots of the cubic polynomial are') , disp (poly_roots)


1.2400 2.5600 5.6400


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disp Simple to use. Provides limited control over appearance ofoutput.

Syntax: disp (variable)

disp (text string)

Examples:>>poly_roots = [ 1.2400 2.5600 5.6400 ]

>> disp ('The roots of the cubic polynomial are')


>> disp (poly_roots)

1.2400 2.5600 5.6400>> disp ('The roots of the cubic polynomial are') , disp (poly_roots)


1.2400 2.5600 5.6400


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Relational and Logical Operators

Operators Description< Less than

> Greater than

= Greater than or equal to

~= Not equal to

== Equal to

& AND

| OR

~ NOT

xor Exclusive OR

-Will output 1 for true conditions and 0 for false conditions

- Can be used with scalars and arrays


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Other Logical built-in functions

Operators Description

all (A)

Returns true if all elements in a vectorA aretrue.

Returns false if one or more elements arefalse

any (A)Returns 1 (true) if any element in a vectorAis true (nonzero).

Returns 0 (false) if all elements are false.

find (A)IfA is a vector, returns the indices of thenonzero elements

find (A>d)IfA is a vector, returns the address of theelements that are larger than d (anyrelational operator can be used)


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SUMMARY

Relational operators involve comparison of two values.

The result of a relational operation is a logical (True/False)

value.

Logical operators combine (or negate) logical values to

produce another logical value.


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Example : Analysis of temp data

The following were the daily max temp in (F) in Washington during

the month of April,2002.58 73 73 53 30 48 56 73 73 66 69 63 74 82 84 91 93 89 91 80

59 69 56 64 63 66 64 74 63 69.

Use relational logical operators to determ ine the fol lowing:

a. The number of days the temp was above 75

b. the number of days the temp was between 65 and 80


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Examples:

>> r = [ 8 12 9 4 23 19 10 ]r =

8 12 9 4 23 19 10

>>s=r>t=r(s) % use sfor addresses in vectorrto create a vector t

t =

8 9 4 10

>> w=r(r


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fprint & sprintf


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Example

function areacircle

r=input('Give radius of circle: ');

a=pi*r^2;

fprintf('The area of circle with radius %.2f is %.6f\n',r,a);

end


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Flow control - selection

The if-elseif-else construction

if elseif elseend

if height>170disp(tall)

elseif height


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Example:

The following script file will returns one of the following messages:teenager, adult and senior given as the input of the variableage.

function check_age

age=input('Enter your age: ')

if age

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