---
name: "zptcon"
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/zptcon.f"
---

# zptcon(3)

Part of [zptcon.f(3)](/zptcon.f/3.md).

## NAME

SRC/zptcon.f

## SYNOPSIS

### Functions/Subroutines

subroutine **zptcon** (n, d, e, anorm, rcond, rwork, info)\
 **ZPTCON**

## Function/Subroutine Documentation

### subroutine zptcon (integer n, double precision, dimension( \* ) d, complex\*16, dimension( \* ) e, double precision anorm, double precision rcond, double precision, dimension( \* ) rwork, integer info)

**ZPTCON**

**Purpose:**

```
!>
!> ZPTCON computes the reciprocal of the condition number (in the
!> 1-norm) of a complex Hermitian positive definite tridiagonal matrix
!> using the factorization A = L*D*L**H or A = U**H*D*U computed by
!> ZPTTRF.
!>
!> Norm(inv(A)) is computed by a direct method, and the reciprocal of
!> the condition number is computed as
!>                  RCOND = 1 / (ANORM * norm(inv(A))).
!>
```

**Parameters**

*N*

```
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>
```

*D*

```
!>          D is DOUBLE PRECISION array, dimension (N)
!>          The n diagonal elements of the diagonal matrix D from the
!>          factorization of A, as computed by ZPTTRF.
!>
```

*E*

```
!>          E is COMPLEX*16 array, dimension (N-1)
!>          The (n-1) off-diagonal elements of the unit bidiagonal factor
!>          U or L from the factorization of A, as computed by ZPTTRF.
!>
```

*ANORM*

```
!>          ANORM is DOUBLE PRECISION
!>          The 1-norm of the original matrix A.
!>
```

*RCOND*

```
!>          RCOND is DOUBLE PRECISION
!>          The reciprocal of the condition number of the matrix A,
!>          computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is the
!>          1-norm of inv(A) computed in this routine.
!>
```

*RWORK*

```
!>          RWORK is DOUBLE PRECISION array, dimension (N)
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Further Details:**

```
!>
!>  The method used is described in Nicholas J. Higham, , SIAM J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.
!>
```

Definition at line **118** of file **zptcon.f**.

## Author

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