Can this be optimized to run faster in MATLAB? - matlab

Question

Here is the code
S = size(shape,3)
shape = 1 - shape;
for i = 2:S
SHAPE = prod(shape(:,:,1:i-1),3);
for c = 1:3
vision(:,:,c,i) = vision(:,:,c,i).*SHAPE;
end
end
output = sum(vision,4);
Maybe there is a way to vectorize it?
And by the way shape and SHAPE are arrays of zeros and ones so they may be somehow used as logicals.

Answer 1

Here's one more bsxfun solution -
S = size(shape,3);
shape = 1 - shape;
SHAPE = cumprod(shape(:,:,1:S-1),3);
vision(:,:,1:3,2:S) = bsxfun(#times,vision(:,:,1:3,2:S),permute(SHAPE,[1 2 4 3]));
output = sum(vision,4);
Tests
Since the code has vision(:,:,c,i) and the iterator c goes from c = 1:3, most likely the third dimension of vision might be 3. To verify that the proposed approach works either way, let's keep it as 5. Also, for proper benchmarking, let's have big numbers on other dimensions and let's have random numbers in them. For verification, at the end we would find the absolute maximum difference between the outputs from the proposed and original approaches.
Benchmarking and output verification code -
% Inputs
shape = rand(150,160,170);
vision = rand(150,160,5,170);
shape = 1 - shape;
S = size(shape,3);
%// Proposed solution :
disp('----------------------- With Proposed solution')
tic
V = vision; %// Make a copy for using with proposed solution
SHAPE = cumprod(shape(:,:,1:S-1),3);
V(:,:,1:3,2:S) = bsxfun(#times,V(:,:,1:3,2:S),permute(SHAPE,[1 2 4 3]));
out = sum(V,4);
toc
%// Original solution :
disp('----------------------- With Original solution')
tic
S = size(shape,3);
for i = 2:S
SHAPE = prod(shape(:,:,1:i-1),3);
for c = 1:3
vision(:,:,c,i) = vision(:,:,c,i).*SHAPE;
end
end
output = sum(vision,4);
toc
error_value = max(abs(output(:) - out(:)))
Command Output -
----------------------- With Proposed solution
Elapsed time is 0.802486 seconds.
----------------------- With Original solution
Elapsed time is 4.401897 seconds.
error_value =
0