Subject: [FFC-dev] Projection - error?

From: Kristian Oelgaard <[email-masked]>
Date: Tue, 20 Jun 2006 08:40:03 +0200

Hi,

I'm trying to project a function defined on a continuous linear basis onto a
discontinuous constant basis.

I use the following form:

P0 = FiniteElement("Discontinuous vector Lagrange", "triangle", 0)
P1 = FiniteElement("Vector Lagrange", "triangle", 1)

v = TestFunction(P0)

u = Function(P1)

pi1 = Projection(P0)

L = dot(v,pi1(u))*dx

The projection matrix generated by FFC looks OK to me, and in Projection.h the
coefficients are:

    const real c0_0 = 3.333333333333333e-01*c[0][0] +
3.333333333333334e-01*c[0][1] + 3.333333333333333e-01*c[0][2];
    const real c0_1 = 3.333333333333333e-01*c[0][3] +
3.333333333333334e-01*c[0][4] + 3.333333333333333e-01*c[0][5];

What is strange is that in the element tensor a factor of 0.5 appears:

    block[0] = 4.999999999999996e-01*G0_0;
    block[1] = 4.999999999999996e-01*G0_1;

So the values of my projection are only half the size of the originals.

Note: In 3D, the factor is 1/6. (These factors appear in monomialintegration.py
as area an volume scaling)

Is there something wrong or am I using projection wrong??

/Kristian