How to avoid nested for loop to make the code faster?
显示 更早的评论
Hi everyone!
Do you have some suggestions to improve the following code?
As it is now, it is very slow…
B_2 = zeros(d,d);
for m = 1:M
for n = m+1 : 2*N
B_2 = B_2 + 4*N^(-1)* A(n) * B(n-m);
end
end
where A(n) and B(n) are 2x2 real, symmetric and full rank, matrices for all possible value of n.
Thanks in advance!
6 个评论
madhan ravi
2019-3-14
编辑：madhan ravi
2019-3-14
Without knowing the values of variables... M , N?
Stef
2019-3-14
I doubt this will gain much speed, but since N appears to be constant you should pull
4*N^(-1)
out of the loops and calculate it once before the loops because it shouldn't change.
Also if A and B are 2x2 matrices how does B(n-m) work? There are only 4 valid indices for a 2x2 matrix so your loop cannot be very long if it only produces values of n and n-m between 1 and 4?
Stephen23
2019-3-14
@Stef: please tell us the values of M, N, and d.
Stef
2019-3-14
Stef
2019-3-14
采纳的回答
Doug Mercer
2019-3-14
If you can generate A and B in a vectorized manner (i.e., for inputs x=[x_1, x_2, ..., x_k] the function A(x) returns a 2x2xk 3D array where a(:, :, i) is the 2x2 array corresponding to x_i) then the following would vectorize the inner loop.
function B_2 = stef()
d = 2;
N = 10^5;
M = sqrt(N);
B_2 = zeros(d,d);
for m = 1:M
n_iter = m+1:2*N;
B_2 = B_2 + 4*N^(-1)*sum(A(n_iter).*B(n_iter - m), 3);
end
function b = B(x)
b = rand(2, 2, length(x));
function a = A(x)
a = rand(2, 2, length(x));
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
