Following up on http://listengine.tuxfamily.org/lists.tuxfamily.org/eigen/2011/02/msg00087.html, just a kindly plea for public BandMatrix functionality compatible with BLAS/LAPACK's notion of general band storage and interoperable when RowMajor is selected. Specifically, I'm after... - Coefficient access - Column and row access - {Super,main,sub,main}-diagonal access - alpha * BandMatrix + beta * BandMatrix with the result of appropriate size (like BLAST report's GB_ACC). - BandMatrix * Vector (like BLAS GBMV) I've tried to play with internal::BandMatrix (and have noticed diagonal access) but haven't had any luck trying to work with it. Gravy would be... - BandMatrix * Matrix (sadly not in BLAS but level 3-ish) - LU factorization and solve a la LAPACK's GBTRF/GBTRS - LU solve handling multiple right hand sizes for BandMatrix^-1 * Matrix ops - Handling of mixed real/complex arithmetic for the above. My driving use case is B-spline collocation-based numerics. These produce discrete operators with small bandwidths. Turns out besides GBMV/GBTRF/GBTRS these operations tend to fall through the cracks. The mixed real/complex is for use in Fourier/B-spline pseudospectral techniques.
Hi, all your requests are obviously planed. To reach these goals, the next step is to introduce the notion of "range vector" which is a column (or a row) where the nonzeros are known to be inside a given range. Then everything should be fairly easy to implement. Actually, the most tricky part is probably: BandMatrix3 = alpha * BandMatrix1 + beta * BandMatrix2; which have to be implemented as: 1 - allocate space in BandMatrix3 and set it to zero 2 - BandMatrix3 += alpha * BandMatrix1 3 - BandMatrix3 += beta * BandMatrix2 With the work in progress refactoring of our expression tree and evaluation mechanism, such an evaluation of BandMatrix3 = alpha * BandMatrix1 + beta * BandMatrix2; should become possible.
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