Having Trouble With Preallocating

When I run my code:

 clear; clc;
 tic
 x=(0:pi/1000000:pi);
 m=zeros(1000000);
 y=sin(x);
  n=1;
  L=length(x);
  while n<L
     m(n,1)=x(n);
     m(n,2)=(y(n+1)-y(n))/(x(n+1)-x(n));
     n=n+1;
 end
 m(n,1)=x(n);
 m(n,2)=NaN;
 toc

I get an error stating: Error using zeros Requested 1000000x1000000 (7450.6GB) array exceeds maximum array size preference. Creation of arrays greater than this limit may take a long time and cause MATLAB to become unresponsive. See array size limit or preference panel for more information.

What should I do about this? I would like to keep the while loops in there and just preallocate if possible. Thanks!

Answer 1

[Stephen23]

m = zeros(1000000,2);

Although a better idea would be to preallocate with the exact required size:

L = numel(x);
m = zeros(L,2);