Matlab tutorial 2 Variables π and sin function

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MATLAB Tutorial 2

Variables

π and sin() function

In the second example the trigonometric function sine and the constant π are used. In MATLAB

they are named sin and pi, respectively.

fun = sin(pi/4)

fun = 0.7071

Numeric format

format long

changes a current format to the format long. To display more digits of the variable fun type

fun

fun = 0.70710678118655

To change a current format to the default one type

format short

fun

fun = 0.7071

In order to display more digits click on File, select Preferences…, and

next select a format you wish to use

To check your variables and format, type

EDU» whos

Name Size Bytes Class

a 1x1 8 double array

fun 1x1 8 double array
Grand total is 2 elements using 16 bytes

To check current variables, type

EDU» who
Your variables are:

a fun

Graphing

To make a graph of y = sin(t) on the interval t = 0 to t = 10 we do the following:

>> t = 0:.3:10;

>> y = sin(t);

>> plot(t,y)

Graphing with m file
Open File and select New>>m file

Type in the following and save the file as chart1.m

t = 0:.3:10;

y = sin(t);

plot(t,y)

Now click Tools>>Run to execute the m file.

(You should see the graph same as the previous one)

Graphing with two variables

Here is how we graph the function, z(x,y) = x exp( - x^2 - y^2):

Type the following into a m file and run it.
[x,y] = meshgrid(-2:.2:2, -2:.2:2);

z = x .* exp(-x.^2 - y.^2);

surf(x,y,z)

Output:

Exercise:
Plot the function f(x) = sin(x)/x with m file. Use grid command to show grid.

Answer:
x = 0:pi/100:10*pi;

y = sin(x)./x;

plot(x,y)

grid

Sorting
To sort an array in ascending or descending order. Use sort() and descsort().

Example:
a = [5,2,4,1,3]

b=sort(a)
c=descsort(a)

Inline Function

Sometimes it is handy to define a function that will be used during the current MATLAB session

only. MATLAB has a command inline used to define the so-called inline functions in the

Command Window.

Let

f = inline('sqrt(x.^2+y.^2)','x','y')

f =

Inline function:

f(x,y) = sqrt(x.^2+y.^2)

You can evaluate this function in a usual way

f(3,4)

ans = 5

Note that this function also works with arrays. Let

A = [1 2;3 4]

A =

1 2

3 4

and

B = ones(2)

B =

1 1

1 1

Then

C = f(A, B)

C =

1.4142 2.2361

3.1623 4.1231

Max() and Min()

To use the maximum or minimum element value of the C array, type

max(C)
min(C)

Exercise:
Use it in a function

f(y)=max(C)*2 + min(C)