MATLAB and Simulink

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To days Outline Functions Strings Sparse Arrays Cell Arrays Structures Exercises on this days topics

MATLAB and Simulink

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Functions files

Runs in its own independent workspace

Receives input data through an Input argument list

Returns data through an Output argument list

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Functions files The first word written in the file must be

the word function function [outarg1,…] = fname(inarg1,…)

%Comment lines…(Executable code)…(return)

MATLAB and Simulink

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Functions files

Variable passing When a function calls occurs.

MATLAB makes a copy of the arguments

If the function modifies the input argument it will not affect the original data in the caller.

This apply both scalars and arrays.

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Example

Create a function that adds a value to the input argument and returns the new value.

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Example

In command window>> A=[1 2];>> B=myfun(A);Input argument before modifying: [1 2]Input argument after modifying: [11 12]>> disp(A) 1 2>> disp(B) 11 12

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Functions files Optional Arguments

Many function supports optional input and output arguments

We have used the plot command with several different Input argument lists.

The max command accepts different output arguments

How do MATLAB functions know how many arguments are present and how do they adjust their behavior?

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Functions files MATLAB offers some special functions to get

information about the arguments and to report errors nargin Returns the actual number of input

arguments used to call the function. nargout Returns the actual number of output

arguments used to call the function. error(msg) Display error message and abort

the function producing the error. warning(msg) Display warning message

Execution can continue nargchk Returns a standard error message if a

function is called with to few or to many arguments

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ExampleThe location of a point in the Cartesian plane can be represented either in rectangular (x,y) or polar coordinates (r,θ).

)cos(rx 22 yxr

)sin(ry xy1tan

• Write a function rect2polar that converts rectangular coordinates to polar coordinates.

• The function is design to support two input arguments (x,y)• However if only one input argument is supplied the functions

should suppose that y is equal to zero.• The function normally returns both magnitude and angle but if

only one output argument is present, it returns only the magnitude

Test the function: In command window:>> [mag,angle]=rect2polar??? Error using ==> rect2polarNot enough input arguments.>> [mag,angle]=rect2polar(1,-1,2)??? Error using ==> rect2polarToo many input arguments.>> [mag,angle]=rect2polar(1)mag =1angle = 0>> [mag,angle]=rect2polar(1,1)mag = 1.4142angle = 45>> [mag]=rect2polar(1,1)mag = 1.4142

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Functions files

Global Memory Provides a way to share data between

functions A global memory is declared with the

global statement. global var1 var2 …

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Functions files

Preserving data When a function finishing executing the

special workspace will be destroyed. Persistent memory

Only accessed within the function A persistent variable is declared using

the persistent statement persistent var1 var2 …

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Functions files

Subfunctions or Internal functions

More than one function in a single file

Top function is the normal function The ones below are subfunctions

or Internal functions

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Strings

In MATLAB a string is an array of type char. str=’This Is a string’

Creating two-dimensional Character arrays Each row must have the same length

MATLAB offers a number of string operations strcmp(str1,str2) Compares two strings

Returns 1 if true. See MATLAB help for more string operations

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Sparse Arrays

Sparse arrays are special arrays in which memory is only allocated for the nonzero elements.

using sparse arrays saves memory and can make a program run faster. sparse(A) Converts A to a sparse

array

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Cell Arrays

A cell array is a special array that can contain different data: Strings Complex numbers vectors

Cell array uses braces {} instead of parentheses () for selecting cells

To view a cell array graphically use cellplot(A)

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Structures Structures can be created in two ways

1. A field at a time using assignment statements.

>>student.name='Carl';>>student.addr='Borlänge';>>student.phone=778858;student = name: 'Carl' addr: 'Borlänge' phone: 778858

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Structures

A second student can be added to the structure by using a subscript

>>student(2).name=’John’; The other field will automatically

be initialized as an empty array. Accessing field in the structure

using parentheses

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Structures

2. All at once using the struct function str_array=struct(field1,val1,field2,val2) Example:

student=struct('Name',{'Carl','John'},'Addr',...

'Borlänge','Falun'},'Phone',{778858,123456})

This will construct a 1x2 structure.

MATLAB and Simulink

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Exercises on this days topics 5.1 , 5.2, 5.10(8) , 5.16(13) ,

5.19(16), 5.24(20) 6.1 , 6.20(18) 7.6

The exercise numbers are referring to the book MATLAB Programming for engineers, third edition 20(second edition).