HELP : Subscript indices must either be real positive integers or logicals - AGAIN

Question

Gobert 2016-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/263376-help-subscript-indices-must-either-be-real-positive-integers-or-logicals-again

评论： Gobert 2016-1-13

I need your help to solve the problem of subscript index that must either be positive integer or logical. Can any one help to correct this ?

A = magic(5);
  M1 = size(A,1);
  M2 = size(A,2);
  E = [5 8 20];
  for x = 1:M1
    for y = 1:M2
    if A(A(x,y) == E)
        A(x-1,y) = 5
      end
    end
    end

Thank you!

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Answer 1

Adam 2016-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/263376-help-subscript-indices-must-either-be-real-positive-integers-or-logicals-again#answer_205794

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By including 'again' in the title I hope that you are learning from previous solutions and that this is a different type of cause to your previous such problems.

The line

A(x-1,y) = 5

fails first time round the loop because x is 1 so x-1 is 0 which is not a valid array index (this is what the error message tells you - it must be a real positive integer or a logical - 0 is neither of those).

How to fix it depends on your intent. Starting your for loop indexed from 2 instead of 1 would remove the error but may not be the solution you want.

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Adam 2016-1-12

编辑：Adam 2016-1-12

在 MATLAB Online 中打开

for x = 2:(M1-1)
   for y = 2:(M2-1)
      for k = 1:length(E)
         if A(A(x,y) == E(k))
            A(x-1,y) = E(k);
            A(x+1,y) = E(k);
            A(x,y-1) = E(k);
            A(x,y+1) = E(k);
         end
      end
   end
end

should probably do the job, though I'm sure there are neater ways.

Gobert 2016-1-13

在 MATLAB Online 中打开

The above code did not unfortunately yield the results expected. See the results, it yielded:

A =
      17     5     5     5    15
       5     5     5     5     5
       5     5     5     5     5
       5     5     5     5     5
      11     5     5     5     9

The expected results are shown below:

   A = 
           17    5     1     8     15
            5     5     5     20    16
            4     5     20    20    20
          10    12    19    20     3
          11    18    25     2     9

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