---
name: "dla_porcond.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/dla_porcond.f"
---

# dla\_porcond.f(3)

## NAME

SRC/dla\_porcond.f

## SYNOPSIS

### Functions/Subroutines

double precision function **dla\_porcond** (uplo, n, a, lda, af, ldaf, cmode, c, info, work, iwork)\
 **DLA\_PORCOND** estimates the Skeel condition number for a symmetric positive-definite matrix.

## Function/Subroutine Documentation

### double precision function dla\_porcond (character uplo, integer n, double precision, dimension( lda, \* ) a, integer lda, double precision, dimension( ldaf, \* ) af, integer ldaf, integer cmode, double precision, dimension( \* ) c, integer info, double precision, dimension( \* ) work, integer, dimension( \* ) iwork)

**DLA\_PORCOND** estimates the Skeel condition number for a symmetric positive-definite matrix.

**Purpose:**

```
!>
!>    DLA_PORCOND 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 triangular factor U or L from the Cholesky factorization
!>     A = U**T*U or A = L*L**T, as computed by DPOTRF.
!>
```

*LDAF*

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

*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.

Definition at line **139** of file **dla\_porcond.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.