# dgtt05.f - Man Page

TESTING/LIN/dgtt05.f

## Synopsis

### Functions/Subroutines

subroutine dgtt05 (trans, n, nrhs, dl, d, du, b, ldb, x, ldx, xact, ldxact, ferr, berr, reslts)
DGTT05

## Function/Subroutine Documentation

### subroutine dgtt05 (character trans, integer n, integer nrhs, double precision, dimension( * ) dl, double precision, dimension( * ) d, double precision, dimension( * ) du, double precision, dimension( ldb, * ) b, integer ldb, double precision, dimension( ldx, * ) x, integer ldx, double precision, dimension( ldxact, * ) xact, integer ldxact, double precision, dimension( * ) ferr, double precision, dimension( * ) berr, double precision, dimension( * ) reslts)

DGTT05

Purpose:

``` DGTT05 tests the error bounds from iterative refinement for the
computed solution to a system of equations A*X = B, where A is a
general tridiagonal matrix of order n and op(A) = A or A**T,
depending on TRANS.

RESLTS(1) = test of the error bound
= norm(X - XACT) / ( norm(X) * FERR )

A large value is returned if this ratio is not less than one.

RESLTS(2) = residual from the iterative refinement routine
= the maximum of BERR / ( NZ*EPS + (*) ), where
(*) = NZ*UNFL / (min_i (abs(op(A))*abs(X) +abs(b))_i )
and NZ = max. number of nonzeros in any row of A, plus 1```
Parameters

TRANS

```          TRANS is CHARACTER*1
Specifies the form of the system of equations.
= 'N':  A * X = B     (No transpose)
= 'T':  A**T * X = B  (Transpose)
= 'C':  A**H * X = B  (Conjugate transpose = Transpose)```

N

```          N is INTEGER
The number of rows of the matrices X and XACT.  N >= 0.```

NRHS

```          NRHS is INTEGER
The number of columns of the matrices X and XACT.  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.```

B

```          B is DOUBLE PRECISION 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).```

X

```          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
The computed solution vectors.  Each vector is stored as a
column of the matrix X.```

LDX

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

XACT

```          XACT is DOUBLE PRECISION array, dimension (LDX,NRHS)
The exact solution vectors.  Each vector is stored as a
column of the matrix XACT.```

LDXACT

```          LDXACT is INTEGER
The leading dimension of the array XACT.  LDXACT >= max(1,N).```

FERR

```          FERR is DOUBLE PRECISION array, dimension (NRHS)
The estimated forward error bounds for each solution vector
X.  If XTRUE is the true solution, FERR bounds the magnitude
of the largest entry in (X - XTRUE) divided by the magnitude
of the largest entry in X.```

BERR

```          BERR is DOUBLE PRECISION array, dimension (NRHS)
The componentwise relative backward error of each solution
vector (i.e., the smallest relative change in any entry of A
or B that makes X an exact solution).```

RESLTS

```          RESLTS is DOUBLE PRECISION array, dimension (2)
The maximum over the NRHS solution vectors of the ratios:
RESLTS(1) = norm(X - XACT) / ( norm(X) * FERR )
RESLTS(2) = BERR / ( NZ*EPS + (*) )```
Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 163 of file dgtt05.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dgtt05(3) is an alias of dgtt05.f(3).

Tue Nov 28 2023 12:08:43 Version 3.12.0 LAPACK