Created attachment 725 [details] Program demonstrating issue See attached program, which triggers an assertion error in debug mode. Assertion error happens when evaluating the product of a dynamically-sized block of a row vector and another matrix into a preallocated matrix (of the correct size).
Also, the results are wrong (with no error or crash) when compiled in release mode (compare c to d in attached program).
The problem is in product_evaluator<Product<Lhs, Rhs, LazyProduct>, ProductTag, DenseShape, DenseShape>::coeff(Index) const where (src/Core/ProductEvaluator, line 535): const Index row = RowsAtCompileTime == 1 ? 0 : index; But in your case RowsAtCompileTime is Dynamic, so the wrong choice is made. A quick-fix would be to use MaxRowsAtCompileTime here, though I'm not entirely sure if this breaks in other situations. Btw: Strangely, it also works with d.noalias() = a_block * b; In this case the coeff(Index, Index) method of the product_evaluator is called (for reasons not obvious to me). Also, this worked in 3.2 --> block3.3
It's rather unusual to call block on a vector. Anyway, here is a quick fix: https://bitbucket.org/eigen/eigen/commits/da70c175e484/ Let me write a full unit test before closing the bug.
I agree, but somebody used this in our codebase and it broke when we updated to the most recent version. Thanks for the fix!
Sure, I was just looking for an excuse on the lack an appropriate unit test, fixed now: https://bitbucket.org/eigen/eigen/commits/3ef64b2fc7e4/ Summary: Bug 1283: add regression unit test
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