Is there some UFL function that could be used instead to select the degree (something that includes spatial coordinates)?
-- Anders On Mon, May 30, 2011 at 08:44:15PM -0000, Martin Sandve Alnæs wrote: > Ok, so NaN was because I manually specified too low degree. > > So we're left with 'auto' which gives a big error: > 0.00666666666667 0.993333333333 8.77744057992e-16 > > This is probably caused by ffc not considering > spatial coordinates in the expression. Fair enough. > > So auto probably chooses 2 for the bilinear form > and 1 for the linear form, keeping the matrix nonsingular > but reducing the accuracy of the right hand side. > > So the only bug here is that FFC could look at > spatial coordinates in the expression for better > autodetection, which would make project() of > expressions in PyDOLFIN more robust. > I'll close this bug and file a blueprint with this point. > > Martin > > On 30 May 2011 22:22, Garth Wells <785...@bugs.launchpad.net> wrote: > > The NaN is not caused by FFC autodetecting the degree. > > > > The numerical error in some cases is due to FFC not increasing the > > degree when the spatial coordinate is used as a coefficient function. > > > > > > Title: > > Projection of x is not accurate > > > > Status in DOLFIN: > > New > > > > Bug description: > > I've tested that projecting x works without the scaling bug that was > > just fixed, using dimensions 1,2,3 and both DG and CG from 0 to 3 > > degrees. I print the max and min values of the vector of the > > projection function, and the values are _close_ to 0 and 1 but not to > > machine precision. The script is below. > > > > There's up to 2.7% error in the 3D case. Is the projection form > > integrated accurately enough? All but the DG0 function space should be > > capable of representing x exactly. Not sure if this is a dolfin or ffc > > bug. > > > > > > from dolfin import * > > > > def mcx(dim): > > if dim == 1: > > mesh = UnitInterval(20) > > cell = interval > > x = cell.x > > if dim == 2: > > mesh = UnitSquare(20, 20) > > cell = triangle > > x = cell.x[0] > > if dim == 3: > > mesh = UnitCube(20, 20, 20) > > cell = tetrahedron > > x = cell.x[0] > > return mesh, cell, x > > > > for dim in range(1, 4): > > mesh, cell, x = mcx(dim) > > minval, maxval = 1.0, 0.0 > > #print dim, "DG" > > for degree in range(3): > > V = FunctionSpace(mesh, "DG", degree) > > u = project(x, V) > > #print dim, degree, u.vector().min(), u.vector().max() > > minval = min(minval, u.vector().min()) > > maxval = max(maxval, u.vector().max()) > > #print dim, "CG" > > for degree in range(1, 4): > > V = FunctionSpace(mesh, "CG", degree) > > u = project(x, V) > > #print dim, degree, u.vector().min(), u.vector().max() > > minval = min(minval, u.vector().min()) > > maxval = max(maxval, u.vector().max()) > > print minval, maxval > > > -- You received this bug notification because you are a member of DOLFIN Team, which is subscribed to DOLFIN. https://bugs.launchpad.net/bugs/785874 Title: Projection of x is not accurate Status in DOLFIN: New Bug description: I've tested that projecting x works without the scaling bug that was just fixed, using dimensions 1,2,3 and both DG and CG from 0 to 3 degrees. I print the max and min values of the vector of the projection function, and the values are _close_ to 0 and 1 but not to machine precision. The script is below. There's up to 2.7% error in the 3D case. Is the projection form integrated accurately enough? All but the DG0 function space should be capable of representing x exactly. Not sure if this is a dolfin or ffc bug. from dolfin import * def mcx(dim): if dim == 1: mesh = UnitInterval(20) cell = interval x = cell.x if dim == 2: mesh = UnitSquare(20, 20) cell = triangle x = cell.x[0] if dim == 3: mesh = UnitCube(20, 20, 20) cell = tetrahedron x = cell.x[0] return mesh, cell, x for dim in range(1, 4): mesh, cell, x = mcx(dim) minval, maxval = 1.0, 0.0 #print dim, "DG" for degree in range(3): V = FunctionSpace(mesh, "DG", degree) u = project(x, V) #print dim, degree, u.vector().min(), u.vector().max() minval = min(minval, u.vector().min()) maxval = max(maxval, u.vector().max()) #print dim, "CG" for degree in range(1, 4): V = FunctionSpace(mesh, "CG", degree) u = project(x, V) #print dim, degree, u.vector().min(), u.vector().max() minval = min(minval, u.vector().min()) maxval = max(maxval, u.vector().max()) print minval, maxval _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
