# Help with debugging some code for the MKLSparse package

**URL:** <https://discourse.julialang.org/t/help-with-debugging-some-code-for-the-mklsparse-package/48764>\
**Category:** Numerics\
**Tags:** debugging\
**Created:** [October 21, 2020, 5:51pm UTC](https://discourse.julialang.org/t/help-with-debugging-some-code-for-the-mklsparse-package/48764 "2020-10-21T17:51:41Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![dmbates](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dmbates/32/44_2.png) [@dmbates](https://discourse.julialang.org/u/dmbates)\
**Post date:** [October 21, 2020, 5:51pm UTC](https://discourse.julialang.org/t/help-with-debugging-some-code-for-the-mklsparse-package/48764/1 "2020-10-21T17:51:41Z")

</div>

On the principle that “given enough eyeballs, all bugs are shallow” I am asking for help in debugging a problem in the `dmb/matrix_sparse` branch of the [`MKLSparse` package](https://github.com/JuliaSparse/MKLSparse.jl).

The purpose of this package is to use Intel’s Mathematics Kernel Library (MKL) for some BLAS (Basic Linear Algebra Subroutines) operations on sparse matrices, as defined in the `SparseArrays` package. Recent versions of MKL allow for a more sophisticated internal representation of different sparse matrix types and correspondingly simpler calling sequences in the so-called [_execution_ routines](https://software.intel.com/content/www/us/en/develop/documentation/mkl-developer-reference-c/top/blas-and-sparse-blas-routines/sparse-blas-level-2-and-level-3-routines/routines-and-supported-operations.html) Constructors for the internal representation were discussed in [Wraping a MKL handle in julia](https://discourse.julialang.org/t/wraping-a-mkl-handle-in-julia/48241) The purpose of this branch is to switch the package from an older formulation of the library to this newer approach.

Right now I have very simple routines for sparse-dense multiplication and solutions of triangular systems implemented. Everything is cool except for one seemingly simple operation - multiplication of a vector by a triangular sparse matrix. The failure shows up in the package tests. The first two testsets have all tests passing but the `triangular` testset has 90 tests passing and 8 failing. The failing tests are all on multiplication of a vector by a triangular matrix or its transpose. The passing tests include exactly the same calculation with the vector replaced by a dense 1-column matrix (`reshape(b, (:, 1))`) and by the same sparse matrix without the triangular property.

Properties like triangularity are passed as a `matrix_descr` struct which I am constructing here from Enum types to follow the pattern in C header file `mkl_sblas.h`. They could just as well be passed as an  
`NTuple{3, Cint}`. I would believe that somehow I had botched those declarations except that the more difficult problem of solving a triangular sparse - dense system works. And multiplication by a triangular sparse matrix works if the right hand operand is a dense matrix instead of a dense vector, resulting in a call to `mkl_sparse_d_mm` instead of `mkl_sparse_d_mv`.

I have spent a couple of days trying to see what I am doing wrong and I can’t. Any insight into what is probably an embarrassingly stupid mistake on my part would be appreciated. Discussion can take place on [https://github.com/JuliaSparse/MKLSparse.jl/issues/25](https://github.com/JuliaSparse/MKLSparse.jl/issues/25)