Help me with this error!

I'm trying to plot x vs y,saving the values in arrays:

clear all;

l = 0.1;

for index = 1:30;

x(index) = (index-1)*0.1;

y(index) = pi*(x.^2 + 1).^2 *l;

end

%PLOT x VERSUS y

plot(x,y);

xlabel('x');

ylabel('pi*((x^2+1)^2)*l');

But I'm getting this error: In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in problem_02 (line 8) y(index) = pi*(x.^2 + 1).^2 *l;

Answer 1

[Roger Stafford]

Instead of:

   y(index) = pi*(x.^2 + 1).^2 *l;

you should write:

   y(index) = pi*(x(index)^2 + 1)^2 *l;

Either that or else you should do:

   y = pi*(x.^2 + 1).^2 *l;

after you exit the for-loop.

As it stands you have a scalar on one side of the equation and a vector on the other side in the original

   y(index) = pi*(x.^2 + 1).^2 *l;

That is what matlab is unhappy about.

[Mobasher Hossain]

Thanks Roger.One more question: I was asked to plot the change in revolution as I rotate function (x^2+1) around x axis,using disk method from 0 to 3 with an increment of 0.1.Now,I summed all y= pi*(x^2 +1)^2 * 0.1 for each x from 0 to 30, and stored those values in arrays.The graph that I'm getting is just on the positive y side(I know because my y function is in squares) but how do I get a 'change in volume' graph when I rotate the function around x axis for x 0 to 3?I think the question is asking me for another graph on the negative y axis,isn't it?I'm very confused!