LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 real function sla_gbrpvgrw ( integer N, integer KL, integer KU, integer NCOLS, real, dimension( ldab, * ) AB, integer LDAB, real, dimension( ldafb, * ) AFB, integer LDAFB )

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

Purpose:
``` SLA_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 REAL 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 REAL array, dimension (LDAFB,N) Details of the LU factorization of the band matrix A, as computed by SGBTRF. 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
September 2012

Definition at line 119 of file sla_gbrpvgrw.f.

119 *
120 * -- LAPACK computational routine (version 3.4.2) --
121 * -- LAPACK is a software package provided by Univ. of Tennessee, --
122 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
123 * September 2012
124 *
125 * .. Scalar Arguments ..
126  INTEGER n, kl, ku, ncols, ldab, ldafb
127 * ..
128 * .. Array Arguments ..
129  REAL ab( ldab, * ), afb( ldafb, * )
130 * ..
131 *
132 * =====================================================================
133 *
134 * .. Local Scalars ..
135  INTEGER i, j, kd
136  REAL amax, umax, rpvgrw
137 * ..
138 * .. Intrinsic Functions ..
139  INTRINSIC abs, max, min
140 * ..
141 * .. Executable Statements ..
142 *
143  rpvgrw = 1.0
144
145  kd = ku + 1
146  DO j = 1, ncols
147  amax = 0.0
148  umax = 0.0
149  DO i = max( j-ku, 1 ), min( j+kl, n )
150  amax = max( abs( ab( kd+i-j, j)), amax )
151  END DO
152  DO i = max( j-ku, 1 ), j
153  umax = max( abs( afb( kd+i-j, j ) ), umax )
154  END DO
155  IF ( umax /= 0.0 ) THEN
156  rpvgrw = min( amax / umax, rpvgrw )
157  END IF
158  END DO
159  sla_gbrpvgrw = rpvgrw
real function sla_gbrpvgrw(N, KL, KU, NCOLS, AB, LDAB, AFB, LDAFB)
SLA_GBRPVGRW computes the reciprocal pivot growth factor norm(A)/norm(U) for a general banded matrix...
Definition: sla_gbrpvgrw.f:119

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