how can i negative all value in a matrix except diagonal?

13.333            5            0            5       3.3333            0
            5       27.333            4           10       3.3333            5
            0            4       17.846            0       3.8462           10
            5           10            0         17.5          2.5            0
       3.3333       3.3333       3.8462          2.5       16.346       3.3333
            0            5           10            0       3.3333       18.333

[Pardomuan Sitompul]

M=M-2*(M-diag(diag(M)))

Answer 1

[Stephen23]

M = [13.333,5,0,5,3.3333,0;5,27.333,4,10,3.3333,5;0,4,17.846,0,3.8462,10;5,10,0,17.5,2.5,0;3.3333,3.3333,3.8462,2.5,16.346,3.3333;0,5,10,0,3.3333,18.333]

M = 6×6

13.3330 5.0000 0 5.0000 3.3333 0 5.0000 27.3330 4.0000 10.0000 3.3333 5.0000 0 4.0000 17.8460 0 3.8462 10.0000 5.0000 10.0000 0 17.5000 2.5000 0 3.3333 3.3333 3.8462 2.5000 16.3460 3.3333 0 5.0000 10.0000 0 3.3333 18.3330

Method one: subtraction (square only):

A = diag(diag(M)) - M.*~eye(size(M))

A = 6×6

13.3330 -5.0000 0 -5.0000 -3.3333 0 -5.0000 27.3330 -4.0000 -10.0000 -3.3333 -5.0000 0 -4.0000 17.8460 0 -3.8462 -10.0000 -5.0000 -10.0000 0 17.5000 -2.5000 0 -3.3333 -3.3333 -3.8462 -2.5000 16.3460 -3.3333 0 -5.0000 -10.0000 0 -3.3333 18.3330

Method two: indexing (more robust, should work for any size):

B = -M;
B(eye(size(M))==1) = diag(M)

B = 6×6

13.3330 -5.0000 0 -5.0000 -3.3333 0 -5.0000 27.3330 -4.0000 -10.0000 -3.3333 -5.0000 0 -4.0000 17.8460 0 -3.8462 -10.0000 -5.0000 -10.0000 0 17.5000 -2.5000 0 -3.3333 -3.3333 -3.8462 -2.5000 16.3460 -3.3333 0 -5.0000 -10.0000 0 -3.3333 18.3330

[arian hoseini]

thanks perfect solution ever.

Answer 2

[Jon]

 Am = -(A - diag(diag(A))) + diag(diag(A))

[Jon]

You could also do it in two lines using

Am = -A
Am(1:7:end) = A(1:7:end)

For both approaches, thanks to earlier posts from @John D'Errico https://www.mathworks.com/matlabcentral/answers/393125-how-to-replace-the-diagonal-entries-of-a-square-matrix-with-entries-from-a-vectore-of-equal-length

and

https://www.mathworks.com/matlabcentral/answers/425937-how-to-multiply-all-values-in-the-diagonal-of-a-matrix-by-1-in-matlab

[arian hoseini]

thank u too