---
name: "dtptri.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/dtptri.f"
---

# dtptri.f(3)

## NAME

SRC/dtptri.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dtptri** (uplo, diag, n, ap, info)\
 **DTPTRI**

## Function/Subroutine Documentation

### subroutine dtptri (character uplo, character diag, integer n, double precision, dimension( \* ) ap, integer info)

**DTPTRI**

**Purpose:**

```
!>
!> DTPTRI computes the inverse of a real upper or lower triangular
!> matrix A stored in packed format.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          = 'U':  A is upper triangular;
!>          = 'L':  A is lower triangular.
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          = 'N':  A is non-unit triangular;
!>          = 'U':  A is unit triangular.
!>
```

*N*

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

*AP*

```
!>          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
!>          On entry, the upper or lower triangular matrix A, stored
!>          columnwise in a linear array.  The j-th column of A is stored
!>          in the array AP as follows:
!>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
!>          if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2) = A(i,j) for j<=i<=n.
!>          See below for further details.
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same packed storage format.
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value
!>          > 0:  if INFO = i, A(i,i) is exactly zero.  The triangular
!>                matrix is singular and its inverse can not be computed.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Further Details:**

```
!>
!>  A triangular matrix A can be transferred to packed storage using one
!>  of the following program segments:
!>
!>  UPLO = 'U':                      UPLO = 'L':
!>
!>        JC = 1                           JC = 1
!>        DO 2 J = 1, N                    DO 2 J = 1, N
!>           DO 1 I = 1, J                    DO 1 I = J, N
!>              AP(JC+I-1) = A(I,J)              AP(JC+I-J) = A(I,J)
!>      1    CONTINUE                    1    CONTINUE
!>           JC = JC + J                      JC = JC + N - J + 1
!>      2 CONTINUE                       2 CONTINUE
!>
```

Definition at line **116** of file **dtptri.f**.

## Author

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