與矩陣乘法的一種可能的解決方案:
n = 9000;
ro = randperm(n,4000);
co = randperm(n , 4000);
A = accumarray([ro(:) co(:)],1);
disp('------matrix multiplication---------:')
tic
[r ,~] = size(A);
B = (1:r) * A;
B(B==0)=r;
toc
disp('------find---------:')
tic
[r,~]=find(A);
B = double(any(A));
B(B==1)= r; B(B==0)=n;
toc
結果:
A = [0 0 0 0 0;
1 0 0 0 0
0 0 0 0 0
0 0 1 0 0
0 0 0 0 1];
[r ,~] = size(A);
B = (1:r) * A;
B(B==0)=r;
與其他方法相比
------matrix multiplication---------:
Elapsed time is 0.0569789 seconds.
------find---------:
Elapsed time is 0.252345 seconds.