stpt01()

subroutine stpt01	(	character	uplo,
		character	diag,
		integer	n,
		real, dimension( * )	ap,
		real, dimension( * )	ainvp,
		real	rcond,
		real, dimension( * )	work,
		real	resid
	)

STPT01

Purpose:

 STPT01 computes the residual for a triangular matrix A times its
 inverse when A is stored in packed format:
    RESID = norm(A*AINV - I) / ( N * norm(A) * norm(AINV) * EPS ),
 where EPS is the machine epsilon.

Parameters

[in]	UPLO	UPLO is CHARACTER*1 Specifies whether the matrix A is upper or lower triangular. = 'U': Upper triangular = 'L': Lower triangular
[in]	DIAG	DIAG is CHARACTER*1 Specifies whether or not the matrix A is unit triangular. = 'N': Non-unit triangular = 'U': Unit triangular
[in]	N	N is INTEGER The order of the matrix A. N >= 0.
[in]	AP	AP is REAL array, dimension (N*(N+1)/2) The original 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.
[in,out]	AINVP	AINVP is REAL array, dimension (N*(N+1)/2) On entry, the (triangular) inverse of the matrix A, packed columnwise in a linear array as in AP. On exit, the contents of AINVP are destroyed.
[out]	RCOND	RCOND is REAL The reciprocal condition number of A, computed as 1/(norm(A) * norm(AINV)).
[out]	WORK	WORK is REAL array, dimension (N)
[out]	RESID	RESID is REAL norm(A*AINV - I) / ( N * norm(A) * norm(AINV) * EPS )

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 107 of file stpt01.f.

*
*  -- LAPACK test routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          DIAG, UPLO
      INTEGER            N
      REAL               RCOND, RESID
*     ..
*     .. Array Arguments ..
      REAL               AINVP( * ), AP( * ), WORK( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO, ONE
      parameter( zero = 0.0e+0, one = 1.0e+0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            UNITD
      INTEGER            J, JC
      REAL               AINVNM, ANORM, EPS
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      REAL               SLAMCH, SLANTP
      EXTERNAL           lsame, slamch, slantp
*     ..
*     .. External Subroutines ..
      EXTERNAL           stpmv
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          real
*     ..
*     .. Executable Statements ..
*
*     Quick exit if N = 0.
*
      IF( n.LE.0 ) THEN
         rcond = one
         resid = zero
         RETURN
      END IF
*
*     Exit with RESID = 1/EPS if ANORM = 0 or AINVNM = 0.
*
      eps = slamch( 'Epsilon' )
      anorm = slantp( '1', uplo, diag, n, ap, work )
      ainvnm = slantp( '1', uplo, diag, n, ainvp, work )
      IF( anorm.LE.zero .OR. ainvnm.LE.zero ) THEN
         rcond = zero
         resid = one / eps
         RETURN
      END IF
      rcond = ( one / anorm ) / ainvnm
*
*     Compute A * AINV, overwriting AINV.
*
      unitd = lsame( diag, 'U' )
      IF( lsame( uplo, 'U' ) ) THEN
         jc = 1
         DO 10 j = 1, n
            IF( unitd )
     $         ainvp( jc+j-1 ) = one
*
*           Form the j-th column of A*AINV
*
            CALL stpmv( 'Upper', 'No transpose', diag, j, ap,
     $                  ainvp( jc ), 1 )
*
*           Subtract 1 from the diagonal
*
            ainvp( jc+j-1 ) = ainvp( jc+j-1 ) - one
            jc = jc + j
   10    CONTINUE
      ELSE
         jc = 1
         DO 20 j = 1, n
            IF( unitd )
     $         ainvp( jc ) = one
*
*           Form the j-th column of A*AINV
*
            CALL stpmv( 'Lower', 'No transpose', diag, n-j+1, ap( jc ),
     $                  ainvp( jc ), 1 )
*
*           Subtract 1 from the diagonal
*
            ainvp( jc ) = ainvp( jc ) - one
            jc = jc + n - j + 1
   20    CONTINUE
      END IF
*
*     Compute norm(A*AINV - I) / (N * norm(A) * norm(AINV) * EPS)
*
      resid = slantp( '1', uplo, 'Non-unit', n, ainvp, work )
*
      resid = ( ( resid*rcond ) / real( n ) ) / eps
*
      RETURN
*
*     End of STPT01
*

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