How to avoid using a loop here?

Question

sznailc 2021-10-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1567238-how-to-avoid-using-a-loop-here

回答： Star Strider 2021-10-19

Hello. I want to do the same thing without a loop.

A = zeros(N);
for m = 1:N
    for n = 1:N
        A(m, n) = 2*N + 1 - (m + n);
    end
end

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Answer 1

Star Strider 2021-10-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1567238-how-to-avoid-using-a-loop-here#answer_811963

在 MATLAB Online 中打开

One approach —

N = 5;
tic
[m,n] = ndgrid(1:N);
A = 2*N + 1 - (m + n)
A = 5×5
     9     8     7     6     5
     8     7     6     5     4
     7     6     5     4     3
     6     5     4     3     2
     5     4     3     2     1
toc
Elapsed time is 0.047132 seconds.

Compare —

tic
A = zeros(N);
for m = 1:N
    for n = 1:N
        A(m, n) = 2*N + 1 - (m + n);
    end
end
toc
Elapsed time is 0.003632 seconds.
A
A = 5×5
     9     8     7     6     5
     8     7     6     5     4
     7     6     5     4     3
     6     5     4     3     2
     5     4     3     2     1