Annotation of rpl/lapack/lapack/dlaqsp.f, revision 1.8
1.8 ! bertrand 1: *> \brief \b DLAQSP
! 2: *
! 3: * =========== DOCUMENTATION ===========
! 4: *
! 5: * Online html documentation available at
! 6: * http://www.netlib.org/lapack/explore-html/
! 7: *
! 8: *> \htmlonly
! 9: *> Download DLAQSP + dependencies
! 10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlaqsp.f">
! 11: *> [TGZ]</a>
! 12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlaqsp.f">
! 13: *> [ZIP]</a>
! 14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlaqsp.f">
! 15: *> [TXT]</a>
! 16: *> \endhtmlonly
! 17: *
! 18: * Definition:
! 19: * ===========
! 20: *
! 21: * SUBROUTINE DLAQSP( UPLO, N, AP, S, SCOND, AMAX, EQUED )
! 22: *
! 23: * .. Scalar Arguments ..
! 24: * CHARACTER EQUED, UPLO
! 25: * INTEGER N
! 26: * DOUBLE PRECISION AMAX, SCOND
! 27: * ..
! 28: * .. Array Arguments ..
! 29: * DOUBLE PRECISION AP( * ), S( * )
! 30: * ..
! 31: *
! 32: *
! 33: *> \par Purpose:
! 34: * =============
! 35: *>
! 36: *> \verbatim
! 37: *>
! 38: *> DLAQSP equilibrates a symmetric matrix A using the scaling factors
! 39: *> in the vector S.
! 40: *> \endverbatim
! 41: *
! 42: * Arguments:
! 43: * ==========
! 44: *
! 45: *> \param[in] UPLO
! 46: *> \verbatim
! 47: *> UPLO is CHARACTER*1
! 48: *> Specifies whether the upper or lower triangular part of the
! 49: *> symmetric matrix A is stored.
! 50: *> = 'U': Upper triangular
! 51: *> = 'L': Lower triangular
! 52: *> \endverbatim
! 53: *>
! 54: *> \param[in] N
! 55: *> \verbatim
! 56: *> N is INTEGER
! 57: *> The order of the matrix A. N >= 0.
! 58: *> \endverbatim
! 59: *>
! 60: *> \param[in,out] AP
! 61: *> \verbatim
! 62: *> AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
! 63: *> On entry, the upper or lower triangle of the symmetric matrix
! 64: *> A, packed columnwise in a linear array. The j-th column of A
! 65: *> is stored in the array AP as follows:
! 66: *> if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
! 67: *> if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
! 68: *>
! 69: *> On exit, the equilibrated matrix: diag(S) * A * diag(S), in
! 70: *> the same storage format as A.
! 71: *> \endverbatim
! 72: *>
! 73: *> \param[in] S
! 74: *> \verbatim
! 75: *> S is DOUBLE PRECISION array, dimension (N)
! 76: *> The scale factors for A.
! 77: *> \endverbatim
! 78: *>
! 79: *> \param[in] SCOND
! 80: *> \verbatim
! 81: *> SCOND is DOUBLE PRECISION
! 82: *> Ratio of the smallest S(i) to the largest S(i).
! 83: *> \endverbatim
! 84: *>
! 85: *> \param[in] AMAX
! 86: *> \verbatim
! 87: *> AMAX is DOUBLE PRECISION
! 88: *> Absolute value of largest matrix entry.
! 89: *> \endverbatim
! 90: *>
! 91: *> \param[out] EQUED
! 92: *> \verbatim
! 93: *> EQUED is CHARACTER*1
! 94: *> Specifies whether or not equilibration was done.
! 95: *> = 'N': No equilibration.
! 96: *> = 'Y': Equilibration was done, i.e., A has been replaced by
! 97: *> diag(S) * A * diag(S).
! 98: *> \endverbatim
! 99: *
! 100: *> \par Internal Parameters:
! 101: * =========================
! 102: *>
! 103: *> \verbatim
! 104: *> THRESH is a threshold value used to decide if scaling should be done
! 105: *> based on the ratio of the scaling factors. If SCOND < THRESH,
! 106: *> scaling is done.
! 107: *>
! 108: *> LARGE and SMALL are threshold values used to decide if scaling should
! 109: *> be done based on the absolute size of the largest matrix element.
! 110: *> If AMAX > LARGE or AMAX < SMALL, scaling is done.
! 111: *> \endverbatim
! 112: *
! 113: * Authors:
! 114: * ========
! 115: *
! 116: *> \author Univ. of Tennessee
! 117: *> \author Univ. of California Berkeley
! 118: *> \author Univ. of Colorado Denver
! 119: *> \author NAG Ltd.
! 120: *
! 121: *> \date November 2011
! 122: *
! 123: *> \ingroup doubleOTHERauxiliary
! 124: *
! 125: * =====================================================================
1.1 bertrand 126: SUBROUTINE DLAQSP( UPLO, N, AP, S, SCOND, AMAX, EQUED )
127: *
1.8 ! bertrand 128: * -- LAPACK auxiliary routine (version 3.4.0) --
1.1 bertrand 129: * -- LAPACK is a software package provided by Univ. of Tennessee, --
130: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8 ! bertrand 131: * November 2011
1.1 bertrand 132: *
133: * .. Scalar Arguments ..
134: CHARACTER EQUED, UPLO
135: INTEGER N
136: DOUBLE PRECISION AMAX, SCOND
137: * ..
138: * .. Array Arguments ..
139: DOUBLE PRECISION AP( * ), S( * )
140: * ..
141: *
142: * =====================================================================
143: *
144: * .. Parameters ..
145: DOUBLE PRECISION ONE, THRESH
146: PARAMETER ( ONE = 1.0D+0, THRESH = 0.1D+0 )
147: * ..
148: * .. Local Scalars ..
149: INTEGER I, J, JC
150: DOUBLE PRECISION CJ, LARGE, SMALL
151: * ..
152: * .. External Functions ..
153: LOGICAL LSAME
154: DOUBLE PRECISION DLAMCH
155: EXTERNAL LSAME, DLAMCH
156: * ..
157: * .. Executable Statements ..
158: *
159: * Quick return if possible
160: *
161: IF( N.LE.0 ) THEN
162: EQUED = 'N'
163: RETURN
164: END IF
165: *
166: * Initialize LARGE and SMALL.
167: *
168: SMALL = DLAMCH( 'Safe minimum' ) / DLAMCH( 'Precision' )
169: LARGE = ONE / SMALL
170: *
171: IF( SCOND.GE.THRESH .AND. AMAX.GE.SMALL .AND. AMAX.LE.LARGE ) THEN
172: *
173: * No equilibration
174: *
175: EQUED = 'N'
176: ELSE
177: *
178: * Replace A by diag(S) * A * diag(S).
179: *
180: IF( LSAME( UPLO, 'U' ) ) THEN
181: *
182: * Upper triangle of A is stored.
183: *
184: JC = 1
185: DO 20 J = 1, N
186: CJ = S( J )
187: DO 10 I = 1, J
188: AP( JC+I-1 ) = CJ*S( I )*AP( JC+I-1 )
189: 10 CONTINUE
190: JC = JC + J
191: 20 CONTINUE
192: ELSE
193: *
194: * Lower triangle of A is stored.
195: *
196: JC = 1
197: DO 40 J = 1, N
198: CJ = S( J )
199: DO 30 I = J, N
200: AP( JC+I-J ) = CJ*S( I )*AP( JC+I-J )
201: 30 CONTINUE
202: JC = JC + N - J + 1
203: 40 CONTINUE
204: END IF
205: EQUED = 'Y'
206: END IF
207: *
208: RETURN
209: *
210: * End of DLAQSP
211: *
212: END
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