## Function Dtrmv

(

**dtrmv** < uplo > < trans > < diag > < n > < a > < lda > < x > < incx > )

Purpose

=======

DTRMV performs one of the matrix-vector operations

x := A*x, or x := A'*x,

where x is an n element vector and A is an n by n unit, or non-unit,

upper or lower triangular matrix.

Parameters

==========

UPLO - CHARACTER*1.

On entry, UPLO specifies whether the matrix is an upper or

lower triangular matrix as follows:

UPLO = 'U' or 'u' A is an upper triangular matrix.

UPLO = 'L' or 'l' A is a lower triangular matrix.

Unchanged on exit.

TRANS - CHARACTER*1.

On entry, TRANS specifies the operation to be performed as

follows:

TRANS = 'N' or 'n' x := A*x.

TRANS = 'T' or 't' x := A'*x.

TRANS = 'C' or 'c' x := A'*x.

Unchanged on exit.

DIAG - CHARACTER*1.

On entry, DIAG specifies whether or not A is unit

triangular as follows:

DIAG = 'U' or 'u' A is assumed to be unit triangular.

DIAG = 'N' or 'n' A is not assumed to be unit

triangular.

Unchanged on exit.

N - INTEGER.

On entry, N specifies the order of the matrix A.

N must be at least zero.

Unchanged on exit.

A - DOUBLE PRECISION array of DIMENSION ( LDA, n ).

Before entry with UPLO = 'U' or 'u', the leading n by n

upper triangular part of the array A must contain the upper

triangular matrix and the strictly lower triangular part of

A is not referenced.

Before entry with UPLO = 'L' or 'l', the leading n by n

lower triangular part of the array A must contain the lower

triangular matrix and the strictly upper triangular part of

A is not referenced.

Note that when DIAG = 'U' or 'u', the diagonal elements of

A are not referenced either, but are assumed to be unity.

Unchanged on exit.

LDA - INTEGER.

On entry, LDA specifies the first dimension of A as declared

in the calling (sub) program. LDA must be at least

max( 1, n ).

Unchanged on exit.

X - DOUBLE PRECISION array of dimension at least

( 1 + ( n - 1 )*abs( INCX ) ).

Before entry, the incremented array X must contain the n

element vector x. On exit, X is overwritten with the

tranformed vector x.

INCX - INTEGER.

On entry, INCX specifies the increment for the elements of

X. INCX must not be zero.

Unchanged on exit.

Level 2 Blas routine.

-- Written on 22-October-1986.

Jack Dongarra, Argonne National Lab.

Jeremy Du Croz, Nag Central Office.

Sven Hammarling, Nag Central Office.

Richard Hanson, Sandia National Labs.