Issue with making an array

Question

Tony 2016-4-23

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/280634-issue-with-making-an-array

评论： Tony 2016-4-24

Here is my code:

   function Tfunc(a,b)
    a = (-(a-1)/a);
    b = (-(b-1)/b);
    for i = 1:30000
      Approximation_b(i) = ((-1)^(1+i)) * ((b^i)/i);
      Approximation_a(i) = ((-1)^(1+i)) * ((a^i)/i);
    end
    sum(Approximation_b)/sum(Approximation_a)
    end

I tried making the following change (2 lines under function):

function Tfunc(a,b)
Approximation_b = zeros(30000);
Approximation_a = zeros(30000);
a = (-(a-1)/a);
b = (-(b-1)/b);
for i = 1:30000
  Approximation_b(i) = ((-1)^(1+i)) * ((b^i)/i);
  Approximation_a(i) = ((-1)^(1+i)) * ((a^i)/i);
end
sum(Approximation_b)/sum(Approximation_a)
end

I thought adding this would help the code run faster since I am creating the array ahead of time, but all I get is a slower code that 1) doesn't run, 2) memory problem.

Why am I getting a memory problem if the first code works just fine?