small trapz clarification needed

I would appreciate some clarification.

I attempt the following:

zz=zeros(1,31);
for xx=linspace(0,30,31);
  x=0:xx;
  y=(c*56e9*3.14e7*(1+x).^2)./(1+(1+x).^2);
  zz(1,xx+1)=trapz(x,y);
end

I get the following errata description:

??? Error using ==> colon
Maximum variable size allowed by the program is exceeded.
Error in ==> trapz at 43
  perm = [dim:max(ndims(y),dim) 1:dim-1];
Error in ==> Cs_kSZ at 14
    eta(1,xx+1)=trapz(x,y);

What is the particular problem?

[the cyclist]

I deleted the duplicate of this question that you posted earlier.

Answer 1

[the cyclist]

[FYI, I put in c=1 to get your code to work at all.]

In the first iteration of your for loop, you are calling trapz() with these inputs:

trapz(0,8.79e17)

which is I suppose you mean to be zero (because you are "integrating" over a single point). However, MATLAB does not handle that case very well, possibly due to floating point error.

I think you might get what you want by skipping that first evaluation, using this modification of your code:

zz=zeros(1,31);
for xx=linspace(1,30,30);
  x=0:xx;
  y=(c*56e9*3.14e7*(1+x).^2)./(1+(1+x).^2);
  zz(1,xx+1)=trapz(x,y);
end