We still haven't decided on the correct strategy for choosing the degree of an unspecified element.
What we have now looks at the total degree of the form and then sets the degree accordingly. This doesn't really work well and the reason is quite simple: We can't figure out the total degree correctly if we don't know the degree of the coefficient. So my new suggestion is the following. We simply scan all elements in the form with specified degrees and set the degree to the maximum degree among the elements. Here are some use cases: 1. v*f*dx If v is an element of degree q, then the degree for the approximation of f is set to q. For quadrature elements, this means that we get a quadrature error in the integral of order q + 1 which in many cases is the same as the convergence of the finite element method. For Lagrange elements, we get an interpolation error when approximating f of degree q + 1 so the situation is the same. 2. v*f*g*dx Same as above here if f and g have unspecified degrees. But if f or g should happen to have a degree higher than q, than that degree will be used for the other coefficient if unspecified. I'll go ahead and make this change in FFC. It's rather easy to change the strategy and FFC is being very verbose about the choices it makes, at least until we have settled on an acceptable strategy. -- Anders
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