inserting an image and plotting it MATLAB

Question

i'm trying to insert an equation and plot it, but i couldn't because i keep getting errors like : matrix dimensions must agree, or inner matrix dimensions must agree.

http://www4.0zz0.com/2012/11/25/10/272913238.png this is the equation. M has a value of 1 to 6 with an increment of 0.5. Q has a value of 0 to 1 with an increment of 0.1.

http://www4.0zz0.com/2012/11/25/10/700692428.png the plot is something like this

 m=1:0.5:6;
 q=0:0.1:1;

i tried to split the equation into parts, so it would be easier for me to insert it, but i'm getting an error with the last part

e=q./m(1-sqrt(1-(q./m).^2));

Subscript indices must either be real positive integers or logicals.

Answer 1

1. To iterate over each combination of m and q: you want to use ndgrid. Right now, both m and q are row vectors, so array-wise operations will only take the first element of m with the first element of q, the second element with the second element, and so on. What you want is a 2D matrix in which m varies along one dimension, and q varies along the other. This is what ndgrid does. Try this:

   [q, m] = ndgrid(0:0.1:1, 1:0.5:6);
   

2. For the subscript indices error message: the problem is multiplication vs. array access. In the equation PNG, the denominator is of the form M{…}, which means M times the value in the braces. In your code, you write m(…), which is actually an array access — not a multiplication. Changing it to m .* (…) makes the code work. The working version is:

   e=q./(m.*(1-sqrt(1-(q./m).^2)));
   

   Now, you can do:

   figure; plot(e);
   

   …and you should get output similar to what you want.