# MATLAB Help

• MATLAB

## Main Question or Discussion Point

Maybe not the proper place to post... but it seems like physics forums is going through some type of "crazy" change right now. Anyways... I'm having trouble finding a website with directions on how to plot a system of equations in MATLAB. If anyone has a basic M-file they could show me, or a tutorial... that'd be really awesome! Thanks for the help :)

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enigma
Staff Emeritus
Gold Member
Code:
x=[-5:.1:5]; % x is a vector containing the numbers -5, -4.9, -4.8, ..., 4.9, 5. Semicolon means don't display to screen
y=4x.^3 - 2x.^2 - 12; % The '.'^ raises each element of the vector to the power listed.
% If you just did ^ it would do matrix multiplication which doesn't work unless the matrix is square.

plot(x,y,'r*') % Plot variable X on the horizontal axis, y on the vertical, and display the points as red stars
Is that what you wanted, or did you need something more?

Actually, I already knew about the plot command. What I didn't know is that you can plot multiple equations with it.

t1=0:.1:10;
t2=10:.1:20;
y1=t1.*1;
y2=t2./t1;

plot(t1,y1,'r-',t2,y2,'r2-',...

But thanks for the reply enigma
Staff Emeritus
Gold Member
Ah, ok.

You can also skip the 'xxx' and have it automatically assign the colors.

Another way to do it is to hold the plot like so:

Code:
figure(1)

plot(x1,y1)

hold on

plot(x2,y2)
plot(x3,y3)

hold off
You can also simply type 'hold' to toggle it.