diagonalise a matrix

[yorkie2010]

Hi everyone,

I have a matrix A = [1 2 3] and would like to diagonalise it so that it becomes:

A = [1 0 0
0 2 0
0 0 3]

I am Matlab user so it can easily be done by using diag(A). But I need to do it in fortran. Does anyone know how to write it in F95? Many thanks in advanced.

Regards,
Vincent

 

[mikrom]

You can write your own simple function or subroutine which takes on input the vector of dimension N (=the matrix diagonal) and returns a diagonal matrix of dimension N x N.
But why should you store the zero elements in memory? It's better to store only the diagonal vector with non zero elements.

 

[xwb]

You can't reshape a 1D array to a 2D array in Fortran. It would have to be something like diag(A, B, N) where A is the 1D array and B is the 2D array. One way, depending on whether your compiler supports matrix operations is

B = 0
do i = 1, N
   B(i,i) = A(i)
end do

 

[yorkie2010]

Thanks a lot guys..Managed to get it to work.