How do I replace "for" loops by matrix multiplication? I am getting confused because of 4 "for" loops. Any suggestions?

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Dhananjay Mishra 2018-10-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423442-how-do-i-replace-for-loops-by-matrix-multiplication-i-am-getting-confused-because-of-4-for-loop

评论： Miriam 2018-10-12

Hello, the code is as follows.

value = zeros();
E2 = zeros();
dxdy = 1;
x1=1;y1=1;u1=1;v1=1;
for u = -1:1:1
     for v = -1:1:1
          for x = -1:1:1
            for y = -1:1:1
               value(x1,y1) = input_data(x1,y1)*exp( ( -1i*k*(((u-x)^2) + (v-y)^2)) / (2*0.2))*(dxdy); 
               y1 = y1+1;
            end
             x1 = x1+1;
             y1 = 1;
          end
              S_rows = sum(value,2);           %Adding components of matrix "value"    
              S_complete = sum(S_rows);
              E2(u1,v1) = S_complete;  
            x1 = 1;
            v1 = v1 + 1;
        end
          u1 = u1+1;
          v1 = 1;
   end
      disp(E2)

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Torsten 2018-10-11

"input_data" must be 27x3, not 3x3.

Dhananjay Mishra 2018-10-12

If you see the program the values of u1 and v1 is reset everytime. Hence the input is 3*3. And the output is also 3*3

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回答（1 个）

Miriam 2018-10-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423442-how-do-i-replace-for-loops-by-matrix-multiplication-i-am-getting-confused-because-of-4-for-loop#answer_341119

编辑：Miriam 2018-10-12

在 MATLAB Online 中打开

dxdy = 1;
[x,y,u,v] = ndgrid(-1:1);
value = input_data.*exp((-1i*k*(((u-x).^2) + (v-y).^2))/(2*0.2))*(dxdy); 
S_rows = sum(value,2);
S_complete = sum(S_rows);
E2 = squeeze(S_complete);
disp(E2)