Subtracting values in a matrix

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Jakub Nosek 2017-11-6

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评论： Jakub Nosek 2017-11-6

Hi, can I just ask you why the code below does not work? I am trying to subtract each value in a row from each other and if the condition is met then add 1 to matrix11(i,j). Apparently there's a problem with matrix10(i,:) expression.

matrix10=[1 7 20; 4 5 6; 7 8 9; 2 5 8]; 
[zk1, zk2] = size(matrix10);
  matrix11=zeros(zk1,zk2);
  for i=1:zk1
      for j=1:zk2
          if (abs(matrix10(i,j) - matrix10(i,:)) >= 2)
              matrix11(i,j)=matrix11(i,j)+1;
          end 
      end
  end 
matrix11 =
       0     0     0
       0     0     0
       0     0     0
       0     0     0

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回答（1 个）

Kaushik Lakshminarasimhan 2017-11-6

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The problem is with this expression in the if statement:

if abs(matrix10(i,j) - matrix10(i,:)) >= 2

The left hand side is a vector but right side is a scalar -- which means that the condition is only met if all 3 differences exceed 2. What is the actual condition you want to check? If it is whether the total sum of differences exceeds 2, then you need to change the statement to:

if sum(abs(matrix10(i,j) - matrix10(i,:))) >= 2

Or it could be something else depending on what your condition actually is.

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Kaushik Lakshminarasimhan 2017-11-6

编辑：Kaushik Lakshminarasimhan 2017-11-6

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If matrix10 and matrix12 have the same number of columns, then you won't need an if statement.

You can do something like:

isTrue1 = (abs(matrix10(i,j) - matrix10(i,:)) >= 2);
isTrue2 = (abs(matrix12(i,j) - matrix12(i,:)) <= 5);
isTrue = (isTrue1 & isTrue2); % if both must be true