向量化訪問數組

Question

是否有矢量化訪問數組重疊段的方法？ 或者最快的方法來做到這一點？

與循環

A=rand(5); 
B=rand(10,5); 
m=6; 
for idx=1:m 
    C(idx)=sum(sum((A(:,:)-B(idx: end-(m+1-idx),:)).^2)); 
end 

Answer 1

這裏最小的樣品是其執行矢量存取使用bsxfun的方法，permute & reshape -

% Size parameters 
m = size(A,1); 
n = size(B,1); 

% Extended version of B, i.e. "B(idx: end-(m+1-idx)+1,:)" across all iterations 
B_ext = B(bsxfun(@plus,(1:m)',0:n-m),:); 

% Perform broadcasted subtraction against A and finally squared summations 
C = sum(sum(bsxfun(@minus,reshape(B_ext,m,n-m+1,[]),permute(A,[1,3,2])).^2,1),3)