Matlab_04a

Simple Graphs

We will start with an easy one, the graph of x squared between -5 and +5:

x = [-5 -4 -3 -2 -1 0 1 2 3 4 5];

y_1 = x.*x; % or x.^2 will also work

plot(x,y_1)

Note that the first line can be expressed in the shorthand:

x = [-5:5];

y_1 = x.*x;

plot(x,y_1)

or to get a graph with more points in the same range we can add the step size to the first line, this goes between the lower and upper value in the range:

x = [-5:0.1:5];

y_1 = x.*x;

plot(x,y_1)

To plot more than one line on the same graph:

x = [-5:0.1:5];

y_1 = x.*x;    % this gives us x squared

y_2 = x.*x.*x; % this gives us x cubed

plot(x,y_1)    % plot the x squared graph

hold on;       % hold the plot for a second line

plot(x,y_2)    % plot x cubed

The trick is the hold on command which holds the same figure open for extra plots. Note that I have added comments (after the percentage signs) which explain what each line does. Anything that comes after a percent sign on the line is ignored by Matlab when it executes instructions.

You can easily add colours to the lines by using r,g,b,c,m,y,k in the plot commands like this:

x = [-5:0.1:5];

y_1 = x.*x;        % this gives us x squared

y_2 = x.*x.*x;     % this gives us x cubed

plot(x,y_1,'r')    % plot the x squared graph

hold on;           % hold the plot for a second line

plot(x,y_2,'g')    % plot x cubed