LAPACK  3.8.0 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.

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.```
Date
December 2016

Definition at line 119 of file zla_gbrpvgrw.f.

119 *
120 * -- LAPACK computational routine (version 3.7.0) --
121 * -- LAPACK is a software package provided by Univ. of Tennessee, --
122 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
123 * December 2016
124 *
125 * .. Scalar Arguments ..
126  INTEGER n, kl, ku, ncols, ldab, ldafb
127 * ..
128 * .. Array Arguments ..
129  COMPLEX*16 ab( ldab, * ), afb( ldafb, * )
130 * ..
131 *
132 * =====================================================================
133 *
134 * .. Local Scalars ..
135  INTEGER i, j, kd
136  DOUBLE PRECISION amax, umax, rpvgrw
137  COMPLEX*16 zdum
138 * ..
139 * .. Intrinsic Functions ..
140  INTRINSIC abs, max, min, REAL, dimag
141 * ..
142 * .. Statement Functions ..
143  DOUBLE PRECISION cabs1
144 * ..
145 * .. Statement Function Definitions ..
146  cabs1( zdum ) = abs( dble( zdum ) ) + abs( dimag( zdum ) )
147 * ..
148 * .. Executable Statements ..
149 *
150  rpvgrw = 1.0d+0
151
152  kd = ku + 1
153  DO j = 1, ncols
154  amax = 0.0d+0
155  umax = 0.0d+0
156  DO i = max( j-ku, 1 ), min( j+kl, n )
157  amax = max( cabs1( ab( kd+i-j, j ) ), amax )
158  END DO
159  DO i = max( j-ku, 1 ), j
160  umax = max( cabs1( afb( kd+i-j, j ) ), umax )
161  END DO
162  IF ( umax /= 0.0d+0 ) THEN
163  rpvgrw = min( amax / umax, rpvgrw )
164  END IF
165  END DO
166  zla_gbrpvgrw = rpvgrw
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:119
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