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Re: Re: [DOLFIN-dev] BLAS mode verified

 

3. It actually matters that the default mode of FFC removes any
products with zeros in the tensor product. BLAS does not know about
zeros.

This seems to be a severe limitation. For PDE systems with Lagrange
elements (the typical case I guess), there will be lots of zeros. From
previous discussions about FFC/Ferari, the conclusion was that
skipping the zero elements was the dominant optimization for computing
the element matrix.


This is exactly why I've been talking about inferring block structure inside the compiler and building a block 3x3 local stiffness matrix (each block might be different). For the vector Laplacian, it's block diagonal, etc. You can combine doing the set of all different blocks with level 3 BLAS (on each element) with getting to throw away all the coarse-grained zeros.

Rob




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