---
name: "ctpt02.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/ctpt02.f"
---

# ctpt02.f(3)

## NAME

TESTING/LIN/ctpt02.f

## SYNOPSIS

### Functions/Subroutines

subroutine **ctpt02** (uplo, trans, diag, n, nrhs, ap, x, ldx, b, ldb, work, rwork, resid)\
 **CTPT02**

## Function/Subroutine Documentation

### subroutine ctpt02 (character uplo, character trans, character diag, integer n, integer nrhs, complex, dimension( \* ) ap, complex, dimension( ldx, \* ) x, integer ldx, complex, dimension( ldb, \* ) b, integer ldb, complex, dimension( \* ) work, real, dimension( \* ) rwork, real resid)

**CTPT02**

**Purpose:**

```
!>
!> CTPT02 computes the residual for the computed solution to a
!> triangular system of linear equations op(A)*X = B, when the
!> triangular matrix A is stored in packed format. The test ratio is
!> the maximum over
!>    norm(b - op(A)*x) / ( ||op(A)||_1 * norm(x) * EPS ),
!> where op(A) = A, A**T, or A**H, b is the column of B, x is the
!> solution vector, and EPS is the machine epsilon.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the matrix A is upper or lower triangular.
!>          = 'U':  Upper triangular
!>          = 'L':  Lower triangular
!>
```

*TRANS*

```
!>          TRANS is CHARACTER*1
!>          Specifies the operation applied to A.
!>          = 'N':  A    * X = B  (No transpose)
!>          = 'T':  A**T * X = B  (Transpose)
!>          = 'C':  A**H * X = B  (Conjugate transpose)
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          Specifies whether or not the matrix A is unit triangular.
!>          = 'N':  Non-unit triangular
!>          = 'U':  Unit triangular
!>
```

*N*

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

*NRHS*

```
!>          NRHS is INTEGER
!>          The number of right hand sides, i.e., the number of columns
!>          of the matrices X and B.  NRHS >= 0.
!>
```

*AP*

```
!>          AP is COMPLEX array, dimension (N*(N+1)/2)
!>          The upper or lower triangular matrix A, packed columnwise in
!>          a linear array.  The j-th column of A is stored in the array
!>          AP as follows:
!>          if UPLO = 'U', AP((j-1)*j/2 + i) = A(i,j) for 1<=i<=j;
!>          if UPLO = 'L',
!>             AP((j-1)*(n-j) + j*(j+1)/2 + i-j) = A(i,j) for j<=i<=n.
!>
```

*X*

```
!>          X is COMPLEX array, dimension (LDX,NRHS)
!>          The computed solution vectors for the system of linear
!>          equations.
!>
```

*LDX*

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

*B*

```
!>          B is COMPLEX array, dimension (LDB,NRHS)
!>          The right hand side vectors for the system of linear
!>          equations.
!>
```

*LDB*

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

*WORK*

```
!>          WORK is COMPLEX array, dimension (N)
!>
```

*RWORK*

```
!>          RWORK is REAL array, dimension (N)
!>
```

*RESID*

```
!>          RESID is REAL
!>          The maximum over the number of right hand sides of
!>          norm(op(A)*B - B) / ( norm(op(A)) * norm(X) * EPS ).
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **145** of file **ctpt02.f**.

## Author

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