X+a*Y with PETSc matrix (Mat)

General Discussion
1

Hi,
As said in the title, I am trying to compute X=X+a*Y where X and Y are Mat PETSc matrices and a is a scalar. Is there a way to do this ? Here a stupid example :

load "PETSc"
mesh Th = square(10,10);
fespace Vh(Th,P1);

varf vX(u,v) = int2d(Th)(u*v) + on(1,u=0);

matrix X = vX(Vh,Vh);
matrix Y = vX(Vh,Vh);

Mat Xp(X);
Mat Yp(Y);
Mat Zp;
real a=2.0;

Yp = a*Xp + Yp;

I see something called MatAXPY in PETSc doc but I don’t know if it is available in FreeFem ? (I see it in PETSc-code.hpp)
I can do it with matrix format and then import the results in Mat but I loose the advantage of distributed matrices in large problem ?
Thanks for your help

2

You are in luck, this feature has been very recently added to FreeFEM develop branch, and it is available in FreeFEM 4.9 (released earlier this week).
You can simply do:

Yp += a*Xp;

Let me know if you need something else.

3

Thank you, I’ve install the 4.9 and now it works.