# mkl_dskymm

Computes matrix-matrix product of a sparse matrix stored using the skyline storage scheme with one-based indexing .

## Syntax

Fortran:

call mkl_dskymm(transa, m, n, k, alpha, matdescra, val, pntr, b, ldb, beta, c, ldc)

C:

mkl_dskymm(&transa, &m, &n, &k, &alpha, matdescra, val, pntr, b, &ldb, &beta, c, &ldc);

## Description

The mkl_dskymm routine performs a matrix-matrix operation defined as
`C := alpha*A*B + beta*C`

or
`C := alpha*A'*B + beta*C,`

where:

alpha and beta are scalars,

B and C are dense matrices, A is an m-by-k sparse matrix in the skyline storage format, A' is the transpose of A.

### Note

This routine supports only one-based indexing of the input arrays.

## Input Parameters

Parameter descriptions are common for all implemented interfaces with the exception of data types that refer here to the FORTRAN 77 standard types. Data types specific to the different interfaces are described in the section “Interfaces” below.

transa

  CHARACTER*1. Specifies the operation.

  If `transa = 'N'` or 'n', then ``C := alpha*A*B + beta*C`,`

  If `transa = 'T'` or 't' or 'C' or 'c', then `C := alpha*A'*B + beta*C`,

m

  INTEGER. Number of rows of the matrix A.

n

  INTEGER. Number of columns of the matrix C.

k

  INTEGER. Number of columns of the matrix A.

alpha

  REAL*8. Specifies the scalar alpha.

matdescra

  CHARACTER. Array of six elements, specifies properties of the matrix used for operation. Only first four array elements are used, their possible values are given in the “Possible Values of the Parameter matdescra”.

  ### Note

  General matrices `(matdescra (1)='G')` is not supported.

val

  REAL*8. Array containing the set of elements of the matrix A in the skyline profile form.

  If `matdescrsa(2)= 'L'`, then val contains elements from the low triangle of the matrix A.

  If `matdescrsa(2)= 'U'`, then val contains elements from the upper triangle of the matrix A.

  Refer to values array description in Skyline Storage Schemefor more details.

pntr

  INTEGER. Array of length `(m+m)` for lower triangle, and `(k+k)` for upper triangle.

  It contains the indices specifying in the val the positions of the first element in each row (column) of the matrix A. Refer to pointers array description in Skyline Storage Scheme for more details.

b

  REAL*8.

  Array, DIMENSION `(ldb, n)`.

  On entry with `transa = 'N'` or 'n', the leading k-by-n part of the array b must contain the matrix B, otherwise the leading m-by-n part of the array b must contain the matrix B.

ldb

  INTEGER. Specifies the first dimension of b as declared in the calling (sub)program.

beta

  REAL*8. Specifies the scalar beta.

c

  REAL*8.

  Array, DIMENSION (ldc, n).

  On entry, the leading m-by-n part of the array c must contain the matrix C, otherwise the leading k-by-n part of the array c must contain the matrix C.

ldc

  INTEGER. Specifies the first dimension of c as declared in the calling (sub)program.

## Output Parameters

c

  Overwritten by the matrix `(alpha*A*B + beta*C)` or `(alpha*A'*B + beta*C)`.

## Interfaces

## FORTRAN 77:

SUBROUTINE mkl_dskymm(transa, m, n, k, alpha, matdescra, val, pntr, b,

ldb, beta, c, ldc)

CHARACTER*1 transa

CHARACTER matdescra(*)

INTEGER m, n, k, ldb, ldc

INTEGER pntr(*)

REAL*8 alpha, beta

REAL*8 val(*), b(ldb,*), c(ldc,*)

## C:

`void mkl_dskymm(char *transa, int *m, int *n, int *k, double *alpha,`
`char *matdescra, double *val, int *pntr, double *b, int *ldb,`
`double *beta, double *c, int *ldc);`

Parent topic: Sparse BLAS Level 2 and Level 3 Routines.