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[Nuno Lopes <question117960@xxxxxxxxxxxxxxxxxxxxx>]

New question #117960 on DOLFIN:
https://answers.launchpad.net/dolfin/+question/117960

Hi, 

I was digging in my code to try to find some  reason  for the  slowdown  I get using  the updated(>0.9.5) versions of dolfin, 
(since the dolfin demos do not reproduce the huge time differences I have in my code).  
I've found that the main issue is the matrix by vector multiplication that I use in some methods .
When using uBLAS backend  I get a huge slowdown compared with PETSc 

In the simple dolfin code below PETSc is at least 40 times faster. 

Is this an expected behavior?

I reproduced the problem in a simple code:

main.cpp:
------------------------------------------------------------------------------
#include <dolfin.h>
#include "TestForm.h"

using namespace dolfin;

int main(int argc, char *argv[])
{
  parameters["linear_algebra_backend"]=argv[1];

  Timer maintimer(argv[1]);
  maintimer.start();
  
  UnitSquare mesh(100,100);
  TestForm::FunctionSpace V(mesh);
  TestForm::BilinearForm  a(V,V);
  TestForm::LinearForm L(V);
  Constant f(1.0);
  L.f=f;

  Matrix A;
  assemble(A,a);

  Vector x;
  assemble(x,L);

  Vector y(x);
  y.zero();

  A.mult(x,y);

  maintimer.stop();
  summary();
}
-----------------------------------------------------------------
with 
TestForm.ufl:
----------------------------------------------------------------
scalar = FiniteElement("Lagrange", "triangle", 1)
v  = TestFunction(scalar)
u1 = TrialFunction(scalar)

f= Coefficient(scalar);

a = v*u1*dx
L =  f*v*dx
------------------------------------------------------------------

using uBLAS approx 2.5s and with PETSc approx 0.06s. 
Could someone please test the code... 

Thanks in advance.
Nuno Lopes.
 

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