Script Matlab

Script Files
Script files simply execute a series of commands when invoked in MATLAB. 
They do not involve the passing of variables. Script files are useful for a variety 
of things such as problem solving and data analysis. Script files are also useful for 
entering a long series of commands that may need corrections.

To create a script file, you must go into your favorite editor and create a file. 
If you want to insert comments into the file, you must use a % symbol at the beginning 
of each line of the comment. Otherwise you type MATLAB commands as you would in the 
MATLAB window. 
For instance, to create a script file called squares.m that would calculate the squares 
from 1 to 30 and plot the number verses its square, you would go into an editor and type: 

		%A script file to calculate the squares from 1 to 30
		%and plot the number verses the square.
		square = [];i = 1;
		while i < 31
		   square(i) = i^2;
		   i = i + 1;

To invoke this file in MATLAB, you would simply type: 

>> squares

MATLAB will then execute the file. The variables used in the file are global variables 
and are therefore accessible in the MATLAB worksheet once the file has been executed. 
This leads to another use of script files, namely storing commonly used variables. 

Sometimes there is a particular matrix or set of data that you will be using several 
times in your work. So that you do not have to retype the matrix or data each time you 
work with MATLAB, you can save the data in a script file. So once again, you must go 
into an editor to create the file. Below is an example of a file called useful.m created 
to store a matrix, its determinant and its inverse. 

		%Matrix A, its determinant, and its inverse
		A = [1 2 3 6 8; 4 2 3 9 10; 15 12 16 14 19;
		    13 12 15 19 23; 27 32 25 28 15];
		DETA = det(A)
		INVA = inv(A)

To bring this matrix and information into the current MATLAB worksheet, you need to type: 

>> useful

The variables A, DETA, and INVA are now accessible to you in MATLAB. 

Function Files
Function files allow you to pass variables for calculating and get a value back. In order 
for an m-file to be a function file, you must type function at the top of the file. 
A function file is useful for when the variables may change and may need to be 
manipulated in a file.

Creating a function file is similar to creating a script file, however you must remember 
to include the word function at the top. It is also important to note that your first 
set of comments that immediately follow the function line are displayed by MATLAB when 
you type help functionname. 
Also the first comment line is what MATLAB uses as a reference when you use the 
lookfor command.

To create a file mean.m that will calculate the mean of an array of numbers, 
you would go into an editor and type: 

		function [mean] = mean(x)
		%To calculate the mean or average of a list
		%x is an array of numbers
		[m,n] = size(x)
		if m == 1
		  m = n;
		mean = sum(x)/m;

To execute this function in MATLAB and to see what happens when you look for it type:

>> w = [67 86 55 98 43 29];
>> [ave] = mean(w)
>> lookfor mean

You can also create functions that return more than one variable. To do this you must put 
the variables in braces following the function command. To create a function stats.m that
returns the mean, standard deviation, and the variance of an array of numbers, go into an 
editor and type: 

		function [mean,stde,var] = stats(x)
		%Mean, Standard Deviation, and Variance
		%For arrays, stats returns the mean, standard
		%deviation and the variance respectively.

		[m,n] = size(x);
		if m == 1
		   m = n;
		mean = sum(x)/m;
		stde = sqrt(sum(x.^2)/m - mean.^2);
		var = stde.^2;

To execute this function in MATLAB, you must assign the function to a vector answer
to display all values found in the function.

>> z = [100 98 45 67 34 54 87 75];
>> [mean,stde,var] = stats(z)
>> help stats

You can also have a function that accepts more than one input. For instance you can 
create a file sumprodinv.m in an editor that takes two matrices and finds their sum, 
product, and the inverse of their product.

		function [Sum,Prod,Inver] = sumprodinv(A,B);
		%Finds the sum, product, and product inverse
		%of two matrices.
		%To use this function assign the output to
		%a vector [sum1,prod1,inv1] = sumprodinv(A,B)

		Sum = A + B;
		Prod = A*B;
		Inver = inv(Prod);

To call this function in MATLAB: 

>> A = [2 3 5; 6 8 9; 4 7 2];
>> B = [5 8 3; 2 9 5; 4 3 0];
>> [sum1,prod1,inv1] = sumprodinv(A,B)