# Re: Intrinsic matmul vs. LAPACK

*From*: rusi_pathan <tabrezali@xxxxxxxxx>*Date*: Wed, 25 May 2011 18:35:56 -0700 (PDT)

On May 25, 1:34 pm, Brad Weir <briar...@xxxxxxxxx> wrote:

Suppose I have a general matrix and a vector and I want to multiply

them. Does anyone know how the performance of the Fortran 90/95

intrinsics (matmul, dot_product, etc.) compare to the LAPACK routines

for general matrices (_gemv, _nrm2, etc.)? What about if the matrix

is symmetric? I would guess that then the special structure of the

matrix makes the LAPACK routines more efficient.

For small matrices the Matmul intrinsic is fine. For large matrices

(in a serial code) you would want a multithreaded BLAS3 like Intel's

MKL. I dont know if Matmul is multithreaded in any of the compilers.

LAPACK is built on top of BLAS so a faster/multithreaded BLAS would

mean a faster LAPACK.

Note: I generally dont work with large dense matrices.

.

**References**:**Intrinsic matmul vs. LAPACK***From:*Brad Weir

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