---
name: "cptt02.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/cptt02.f"
---

# cptt02.f(3)

## NAME

TESTING/LIN/cptt02.f

## SYNOPSIS

### Functions/Subroutines

subroutine **cptt02** (uplo, n, nrhs, d, e, x, ldx, b, ldb, resid)\
 **CPTT02**

## Function/Subroutine Documentation

### subroutine cptt02 (character uplo, integer n, integer nrhs, real, dimension( \* ) d, complex, dimension( \* ) e, complex, dimension( ldx, \* ) x, integer ldx, complex, dimension( ldb, \* ) b, integer ldb, real resid)

**CPTT02**

**Purpose:**

```
!>
!> CPTT02 computes the residual for the solution to a symmetric
!> tridiagonal system of equations:
!>    RESID = norm(B - A*X) / (norm(A) * norm(X) * EPS),
!> where EPS is the machine epsilon.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the superdiagonal or the subdiagonal of the
!>          tridiagonal matrix A is stored.
!>          = 'U':  E is the superdiagonal of A
!>          = 'L':  E is the subdiagonal of A
!>
```

*N*

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

*NRHS*

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

*D*

```
!>          D is REAL array, dimension (N)
!>          The n diagonal elements of the tridiagonal matrix A.
!>
```

*E*

```
!>          E is COMPLEX array, dimension (N-1)
!>          The (n-1) subdiagonal elements of the tridiagonal matrix A.
!>
```

*X*

```
!>          X is COMPLEX array, dimension (LDX,NRHS)
!>          The n by nrhs matrix of solution vectors X.
!>
```

*LDX*

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

*B*

```
!>          B is COMPLEX array, dimension (LDB,NRHS)
!>          On entry, the n by nrhs matrix of right hand side vectors B.
!>          On exit, B is overwritten with the difference B - A*X.
!>
```

*LDB*

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

*RESID*

```
!>          RESID is REAL
!>          norm(B - A*X) / (norm(A) * norm(X) * EPS)
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **114** of file **cptt02.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.