How do I plot this non-linear function...

This question is pretty elementary, but I'm new to MATLAB and am having trouble with this. I want two curves, one of r vs. T (which is easy, it's just a fourth power function) and one of r2 vs. T (on the same graph). That's fine, except r2 is r multiplied by some function of T (which will be on the x-axis) that I called k.

T=180:1:360
k=.8823-((T-179)*(.0039))
s=1.1e-2
r=s*(T.^4)
r2=k*s*(T.^4)

plot(T,r,'-k',T,r2)

This doesn't work...This is just an example, but my head still isn't around the matrix interpretation of plotting, so any tips for plotting stuff like this or non-linear functions in general would be appreciated

Answer 1

[Matt Fig]

One minor change will make it work.

    T = 180:1:360;
    k = .8823-((T-179)*(.0039));
    s = 1.1e-2;
    r = s*(T.^4);
    r2 = k.*s.*(T.^4);  % Or  r2 = k.*(s*(T.^4)); Or  r2=(k*s).*(T.^4);
    plot(T,r,'-k',T,r2)

In general, whenever you have two or more vectors and you want their product to be a vector, use element-by-element multiplication (include the dot). Look at a small example:

a = 1:3
b = 5:7
a.*b

The same goes for division and exponentiation.

Answer 2

[Matt Tearle]

You should be getting an error on the line that defines r2 (before you even get to the plot). As Matt Fig points out, the multiplication there should be .* (element-wise), not *.