# dla_syrcond.f man page

dla_syrcond.f

## Synopsis

### Functions/Subroutines

double precision function **dla_syrcond** (UPLO, **N**, A, **LDA**, AF, LDAF, IPIV, CMODE, C, INFO, WORK, IWORK)**DLA_SYRCOND** estimates the Skeel condition number for a symmetric indefinite matrix.

## Function/Subroutine Documentation

### double precision function dla_syrcond (character UPLO, integer N, double precision, dimension( lda, * ) A, integer LDA, double precision, dimension( ldaf, * ) AF, integer LDAF, integer, dimension( * ) IPIV, integer CMODE, double precision, dimension( * ) C, integer INFO, double precision, dimension( * ) WORK, integer, dimension( * ) IWORK)

**DLA_SYRCOND** estimates the Skeel condition number for a symmetric indefinite matrix.

**Purpose:**

DLA_SYRCOND estimates the Skeel condition number of op(A) * op2(C) where op2 is determined by CMODE as follows CMODE = 1 op2(C) = C CMODE = 0 op2(C) = I CMODE = -1 op2(C) = inv(C) The Skeel condition number cond(A) = norminf( |inv(A)||A| ) is computed by computing scaling factors R such that diag(R)*A*op2(C) is row equilibrated and computing the standard infinity-norm condition number.

**Parameters:**-
*UPLO*UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.

*N*N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.

*A*A is DOUBLE PRECISION array, dimension (LDA,N) On entry, the N-by-N matrix A.

*LDA*LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).

*AF*AF is DOUBLE PRECISION array, dimension (LDAF,N) The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by DSYTRF.

*LDAF*LDAF is INTEGER The leading dimension of the array AF. LDAF >= max(1,N).

*IPIV*IPIV is INTEGER array, dimension (N) Details of the interchanges and the block structure of D as determined by DSYTRF.

*CMODE*CMODE is INTEGER Determines op2(C) in the formula op(A) * op2(C) as follows: CMODE = 1 op2(C) = C CMODE = 0 op2(C) = I CMODE = -1 op2(C) = inv(C)

*C*C is DOUBLE PRECISION array, dimension (N) The vector C in the formula op(A) * op2(C).

*INFO*INFO is INTEGER = 0: Successful exit. i > 0: The ith argument is invalid.

*WORK*WORK is DOUBLE PRECISION array, dimension (3*N). Workspace.

*IWORK*IWORK is INTEGER array, dimension (N). Workspace.

**Author:**-
Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

Definition at line 150 of file dla_syrcond.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dla_syrcond(3) is an alias of dla_syrcond.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK