LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ zla_gbrpvgrw()

double precision function zla_gbrpvgrw ( integer  N,
integer  KL,
integer  KU,
integer  NCOLS,
complex*16, dimension( ldab, * )  AB,
integer  LDAB,
complex*16, dimension( ldafb, * )  AFB,
integer  LDAFB 
)

ZLA_GBRPVGRW computes the reciprocal pivot growth factor norm(A)/norm(U) for a general banded matrix.

Download ZLA_GBRPVGRW + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 ZLA_GBRPVGRW computes the reciprocal pivot growth factor
 norm(A)/norm(U). The "max absolute element" norm is used. If this is
 much less than 1, the stability of the LU factorization of the
 (equilibrated) matrix A could be poor. This also means that the
 solution X, estimated condition numbers, and error bounds could be
 unreliable.
Parameters
[in]N
          N is INTEGER
     The number of linear equations, i.e., the order of the
     matrix A.  N >= 0.
[in]KL
          KL is INTEGER
     The number of subdiagonals within the band of A.  KL >= 0.
[in]KU
          KU is INTEGER
     The number of superdiagonals within the band of A.  KU >= 0.
[in]NCOLS
          NCOLS is INTEGER
     The number of columns of the matrix A.  NCOLS >= 0.
[in]AB
          AB is COMPLEX*16 array, dimension (LDAB,N)
     On entry, the matrix A in band storage, in rows 1 to KL+KU+1.
     The j-th column of A is stored in the j-th column of the
     array AB as follows:
     AB(KU+1+i-j,j) = A(i,j) for max(1,j-KU)<=i<=min(N,j+kl)
[in]LDAB
          LDAB is INTEGER
     The leading dimension of the array AB.  LDAB >= KL+KU+1.
[in]AFB
          AFB is COMPLEX*16 array, dimension (LDAFB,N)
     Details of the LU factorization of the band matrix A, as
     computed by ZGBTRF.  U is stored as an upper triangular
     band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1,
     and the multipliers used during the factorization are stored
     in rows KL+KU+2 to 2*KL+KU+1.
[in]LDAFB
          LDAFB is INTEGER
     The leading dimension of the array AFB.  LDAFB >= 2*KL+KU+1.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 115 of file zla_gbrpvgrw.f.

117 *
118 * -- LAPACK computational routine --
119 * -- LAPACK is a software package provided by Univ. of Tennessee, --
120 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
121 *
122 * .. Scalar Arguments ..
123  INTEGER N, KL, KU, NCOLS, LDAB, LDAFB
124 * ..
125 * .. Array Arguments ..
126  COMPLEX*16 AB( LDAB, * ), AFB( LDAFB, * )
127 * ..
128 *
129 * =====================================================================
130 *
131 * .. Local Scalars ..
132  INTEGER I, J, KD
133  DOUBLE PRECISION AMAX, UMAX, RPVGRW
134  COMPLEX*16 ZDUM
135 * ..
136 * .. Intrinsic Functions ..
137  INTRINSIC abs, max, min, real, dimag
138 * ..
139 * .. Statement Functions ..
140  DOUBLE PRECISION CABS1
141 * ..
142 * .. Statement Function Definitions ..
143  cabs1( zdum ) = abs( dble( zdum ) ) + abs( dimag( zdum ) )
144 * ..
145 * .. Executable Statements ..
146 *
147  rpvgrw = 1.0d+0
148 
149  kd = ku + 1
150  DO j = 1, ncols
151  amax = 0.0d+0
152  umax = 0.0d+0
153  DO i = max( j-ku, 1 ), min( j+kl, n )
154  amax = max( cabs1( ab( kd+i-j, j ) ), amax )
155  END DO
156  DO i = max( j-ku, 1 ), j
157  umax = max( cabs1( afb( kd+i-j, j ) ), umax )
158  END DO
159  IF ( umax /= 0.0d+0 ) THEN
160  rpvgrw = min( amax / umax, rpvgrw )
161  END IF
162  END DO
163  zla_gbrpvgrw = rpvgrw
164 *
165 * End of ZLA_GBRPVGRW
166 *
double precision function zla_gbrpvgrw(N, KL, KU, NCOLS, AB, LDAB, AFB, LDAFB)
ZLA_GBRPVGRW computes the reciprocal pivot growth factor norm(A)/norm(U) for a general banded matrix.
Definition: zla_gbrpvgrw.f:117
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