The code is strange, because all elements of A are 0 except for the first one. B(1) is zero, so prod(B(1:n)) is zeros also. Maybe you mean:
n = 10000;
B = linspace(1,100,n); % Not starting at 0
tic
A = zeros(n, 1);
for i = 1:n
A(i) = prod(B(1:i-1));
end
toc
% Alternative: A naive loop avoiding repeated work:
tic
D = zeros(n, 1);
c = 1;
for i = 1:n
D(i) = c;
c = c * B(i);
end
toc
% Faster:
tic
C = [1, cumprod(B(1:n - 1))].';
toc
Even the loop is much faster than calculating the product from scratch in each iteration again. cumprod is much faster again.
