# mkl_dbsrmm

Computes matrix - matrix product of a sparse matrix stored in the BSR format.

## Syntax

Fortran:

call mkl_dbsrmm(transa, m, n, k, lb, alpha, matdescra, val, indx, pntrb, pntre, b, ldb, beta, c, ldc)

C:

mkl_dbsrmm(&transa, &m, &n, &k, &lb, &alpha, matdescra, val, indx, pntrb, pntre, b, &ldb, &beta, c, &ldc);

## Description

The mkl_dbsrmm 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 block sparse row (BSR) format, A' is the transpose of A.

### Note

This routine supports BSR format both with one-based indexing and zero-based indexing.

## Input Parameters

Parameter descriptions are common for all implemented interfaces with the exception of data types that
`dfdfdfdfdfdfd`
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 the matrix-matrix product is computed as `C := alpha*A*B + beta*C`

  If `transa = 'T'` or 't' or 'C' or 'c', then the matrix-vector product is computed as `C := alpha*A'*B + beta*C`,

m

  INTEGER. Number of block rows of the matrix A.

n

  INTEGER. Number of columns of the matrix C.

k

  INTEGER. Number of block columns of the matrix A.

lb

  INTEGER. Size of the block in 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”.

val

  REAL*8. Array containing elements of non-zero blocks of the matrix A. Its length is equal to the number of non-zero blocks in the matrix A multiplied by `lb*lb`. Refer to the values array description in BSR Format for more details.

indx

  INTEGER. Array containing the column indices for each non-zero block in the matrix A. Its length is equal to the number of non-zero blocks in the matrix A. Refer to the columns array description in BSR Format for more details.

pntrb

  INTEGER. Array of length m.

  For one-based indexing: this array contains row indices, such that `pntrb(i) - pntrb(1)+1` is the first index of block row i in the array indx.

  For zero-based indexing: this array contains row indices, such that `pntrb(i) - pntrb(0)` is the first index of block row i in the array indx.

  Refer to pointerB array description in BSR Format for more details.

pntre

  INTEGER. Array of length m.

  For one-based intexing this array contains row indices, such that `pntre(i) - pntrb(1)` is the last index of block row i in the array indx.

  For zero-based intexing this array contains row indices, such that `pntre(i) - pntrb(0)-1` is the last index of block row i in the array indx.

  Refer to pointerE array description in BSR Format for more details.

b

  REAL*8.

  Array, DIMENSION `(ldb, n)` for one-based indexing, DIMENSION `(m, ldb)` for zero-based indexing.

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

ldb

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

beta

  REAL*8. Specifies the scalar beta.

c

  REAL*8.

  Array, DIMENSION `(ldc, n)` for one-based indexing, DIMENSION `(k, ldc)` for zero-based indexing.

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

ldc

  INTEGER. Specifies the firstcbbcbbcbcb dimension (in blocks) 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_dbsrmm(transa, m, n, k, lb, alpha, matdescra, val,

indx, pntrb, pntre, b, ldb, beta, c, ldc)

CHARACTER*1 transa

CHARACTER matdescra(*)

INTEGER m, n, k, ld, ldb, ldc

INTEGER indx(*), pntrb(m), pntre(m)

REAL*8 alpha, beta

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

## C:

`void mkl_dbsrmm(char *transa, int *m, int *n, int *k, int *lb,`
`double *alpha, char *matdescra, double *val, int *indx, int *pntrb,`
`int *pntre, double *b, int *ldb, double *beta, double *c, int *ldc,);`

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