#### Matlab Programs, Function Programs and Script Programs

Matlab Programs:

In Mat lab, programs may be written as well as saved in files with a suffix .m called M-files. There aretwo kinds of M-file programs: functions as well as scripts.

Function Programs:

Start by clicking on the new document icon in the top left of the Mat lab window (it looks like anempty sheet of paper).

In the document window enter the following:

function y = myfunc(x)

y = 2*x.^2 - 3*x + 1;

Save this file as- myfunc.m in your working directory. This file is able to now be used in the commandwindow just like any predefined Mat labfunction in the command window enters:

> x = -2:.1:2; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Produces a vector of x values.
> y = myfunc(x); . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Produces a vector of y values.
>plot(x,y)

Note that the fact we used x also y in both the function program and in the command window wasjust a coincidence. In reality it is the name of the file myfunc.m that actually mattered not whatanything in it was called. We could merely as well have made the function

function nonsense = yourfunc(inputvector)
nonsense = 2*inputvector.^2 - 3*inputvector + 1;

Glance back at the program. All function programs are similar to this one, the necessary elements are:

• There are inputs as well as outputs.
• The outputs name of the function as well as the inputs must appear in the first line.
• The body of the program should assign values to the outputs.

Functions are able to have multiple inputs and/or multiple outputs. Subsequently let’s create a function that has 1input and 3 output variables. Open a new document in addition to type:

function [x2 x3 x4] = mypowers(x)
x2 = x.^2;
x3 = x.^3;
x4 = x.^4;

Save this file as mypowers.m. In the command window we are able to use the results of the program tomake graphs

> x = -1:.1:1
> [x2 x3 x4] = mypowers(x);
> plot(x,x,’black’,x,x2,’blue’,x,x3,’green’,x,x4,’red’)

Script Programs:

Mat lab uses a second kind of program that differs from a function program in several ways namely:

• There are no inputs as well as outputs.
• A script program may perhaps use as well as change variables in the current workspace (the variables utilizedby the command window.)

Below is a script program that completes the similar thing as the function program plus thecommands in the previous section:

x2 = x.^2;
x3 = x.^3;
x4 = x.^4;
plot(x,x,’black’,x,x2,’blue’,x,x3,’green’,x,x4,’red’)

Write this program into a new document and save it as mygraphs.m. In the command window write:

> x = -1:.1:1;
>mygraphs

Note that the program utilized the variable x in its calculations even though x was defined in thecommand window not in the program.

Several people use script programs for routine calculations that would require typing more than onecommand in the command window.

They do this for the reason that correcting mistakes is easier in a programthan in the command window.

For programs that have extra than a couple of lines it is important to include comments. Commentspermit other people to know what your program does and they as well remind yourself what yourprogram does if you set it aside and come back to it later. It is best to comprise comments not onlyat the top of a program, but as well with each section. In Mat lab anything that comes in a line aftera % is a comment.

For a function program the comments must at least give the purpose, inputs, and outputs. Anappropriately commented version of the function with which we started this section is-

function y = myfunc(x)
% Computes the function 2x^2 -3x +1
% Input: x -- a number or vector; for a vector the computation is elementwise
% Output: y -- a number or vector of the same size as x
y = 2*x.^2 - 3*x + 1;

For a script program it is habitually helpful to comprise the name of the program at the beginning. Forillustration:

% mygraphs
% plots the graphs of x, x^2, x^3, and x^4
% on the interval [-1,1]
% fix the domain and evaluation points
x = -1:.1:1;
% calculate powers
% x1 is just x
x2 = x.^2;
x3 = x.^3;
x4 = x.^4;
% plot each of the graphs
plot(x,x,’black’,x,x2,’blue’,x,x3,’green’,x,x4,’red’)

The Mat lab command assists prints the primary block of comments from a file. If we save the above asmygraphs.m and after that do

> help mygraphs

It will print into the command window:

mygraphs
plots the graphs of x, x^2, x^3, and x^4
on the interval [-1,1]

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