---
name: "dgtt02.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/dgtt02.f"
---

# dgtt02.f(3)

## NAME

TESTING/LIN/dgtt02.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dgtt02** (trans, n, nrhs, dl, d, du, x, ldx, b, ldb, resid)\
 **DGTT02**

## Function/Subroutine Documentation

### subroutine dgtt02 (character trans, integer n, integer nrhs, double precision, dimension( \* ) dl, double precision, dimension( \* ) d, double precision, dimension( \* ) du, double precision, dimension( ldx, \* ) x, integer ldx, double precision, dimension( ldb, \* ) b, integer ldb, double precision resid)

**DGTT02**

**Purpose:**

```
!>
!> DGTT02 computes the residual for the solution to a tridiagonal
!> system of equations:
!>    RESID = norm(B - op(A)*X) / (norm(op(A)) * norm(X) * EPS),
!> where EPS is the machine epsilon.
!> The norm used is the 1-norm.
!>
```

**Parameters**

*TRANS*

```
!>          TRANS is CHARACTER
!>          Specifies the form of the residual.
!>          = 'N':  B - A    * X  (No transpose)
!>          = 'T':  B - A**T * X  (Transpose)
!>          = 'C':  B - A**H * X  (Conjugate transpose = Transpose)
!>
```

*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 B and X.  NRHS >= 0.
!>
```

*DL*

```
!>          DL is DOUBLE PRECISION array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of A.
!>
```

*D*

```
!>          D is DOUBLE PRECISION array, dimension (N)
!>          The diagonal elements of A.
!>
```

*DU*

```
!>          DU is DOUBLE PRECISION array, dimension (N-1)
!>          The (n-1) super-diagonal elements of A.
!>
```

*X*

```
!>          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
!>          The computed solution vectors X.
!>
```

*LDX*

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

*B*

```
!>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
!>          On entry, the right hand side vectors for the system of
!>          linear equations.
!>          On exit, B is overwritten with the difference B - op(A)*X.
!>
```

*LDB*

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

*RESID*

```
!>          RESID is DOUBLE PRECISION
!>          norm(B - op(A)*X) / (norm(op(A)) * norm(X) * EPS)
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **123** of file **dgtt02.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.