dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

jesperc wrote:
> Hi,
>
> Does anyone have an example of using the ident() function in 
> PETScMatrix. I cannot get it to work 

Matrix::ident(. . . ) is not meant to do this, so it is unlikely to work.

and using a for loop with set() to
> create an identity matrix is painfully slow...
>
> This is how I do it now:
>
> Matrix A;
> A.init(n,n,1);
> for (int i=0; i<n; ++i)
>    A.set(i,i,1);

You shouldn't set Matrix values element-wise (Matrix::set(int,int,real) 
has been removed from the Matrix interface to stop users doing this). If 
you really want to access matrix entries element-wise, use a 
uBlasMatrix, otherwise set values in large blocks using

  Matrix::set(const real* block, uint m, const uint* rows, uint n, 
const uint* cols)

Garth

> and it kills me/my computer.
>
> Kind regards, Jesper
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