LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
dsyswapr.f
Go to the documentation of this file.
1 *> \brief \b DSYSWAPR applies an elementary permutation on the rows and columns of a symmetric matrix.
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 *> \htmlonly
10 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dsyswapr.f">
11 *> [TGZ]</a>
12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dsyswapr.f">
13 *> [ZIP]</a>
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dsyswapr.f">
15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE DSYSWAPR( UPLO, N, A, LDA, I1, I2)
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER UPLO
25 * INTEGER I1, I2, LDA, N
26 * ..
27 * .. Array Arguments ..
28 * DOUBLE PRECISION A( LDA, N )
29 *
30 *
31 *> \par Purpose:
32 * =============
33 *>
34 *> \verbatim
35 *>
36 *> DSYSWAPR applies an elementary permutation on the rows and the columns of
37 *> a symmetric matrix.
38 *> \endverbatim
39 *
40 * Arguments:
41 * ==========
42 *
43 *> \param[in] UPLO
44 *> \verbatim
45 *> UPLO is CHARACTER*1
46 *> Specifies whether the details of the factorization are stored
47 *> as an upper or lower triangular matrix.
48 *> = 'U': Upper triangular, form is A = U*D*U**T;
49 *> = 'L': Lower triangular, form is A = L*D*L**T.
50 *> \endverbatim
51 *>
52 *> \param[in] N
53 *> \verbatim
54 *> N is INTEGER
55 *> The order of the matrix A. N >= 0.
56 *> \endverbatim
57 *>
58 *> \param[in,out] A
59 *> \verbatim
60 *> A is DOUBLE PRECISION array, dimension (LDA,N)
61 *> On entry, the NB diagonal matrix D and the multipliers
62 *> used to obtain the factor U or L as computed by DSYTRF.
63 *>
64 *> On exit, if INFO = 0, the (symmetric) inverse of the original
65 *> matrix. If UPLO = 'U', the upper triangular part of the
66 *> inverse is formed and the part of A below the diagonal is not
67 *> referenced; if UPLO = 'L' the lower triangular part of the
68 *> inverse is formed and the part of A above the diagonal is
69 *> not referenced.
70 *> \endverbatim
71 *>
72 *> \param[in] LDA
73 *> \verbatim
74 *> LDA is INTEGER
75 *> The leading dimension of the array A. LDA >= max(1,N).
76 *> \endverbatim
77 *>
78 *> \param[in] I1
79 *> \verbatim
80 *> I1 is INTEGER
81 *> Index of the first row to swap
82 *> \endverbatim
83 *>
84 *> \param[in] I2
85 *> \verbatim
86 *> I2 is INTEGER
87 *> Index of the second row to swap
88 *> \endverbatim
89 *
90 * Authors:
91 * ========
92 *
93 *> \author Univ. of Tennessee
94 *> \author Univ. of California Berkeley
95 *> \author Univ. of Colorado Denver
96 *> \author NAG Ltd.
97 *
98 *> \date September 2012
99 *
100 *> \ingroup doubleSYauxiliary
101 *
102 * =====================================================================
103  SUBROUTINE dsyswapr( UPLO, N, A, LDA, I1, I2)
104 *
105 * -- LAPACK auxiliary routine (version 3.4.2) --
106 * -- LAPACK is a software package provided by Univ. of Tennessee, --
107 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
108 * September 2012
109 *
110 * .. Scalar Arguments ..
111  CHARACTER uplo
112  INTEGER i1, i2, lda, n
113 * ..
114 * .. Array Arguments ..
115  DOUBLE PRECISION a( lda, n )
116 *
117 * =====================================================================
118 *
119 * ..
120 * .. Local Scalars ..
121  LOGICAL upper
122  INTEGER i
123  DOUBLE PRECISION tmp
124 *
125 * .. External Functions ..
126  LOGICAL lsame
127  EXTERNAL lsame
128 * ..
129 * .. External Subroutines ..
130  EXTERNAL dswap
131 * ..
132 * .. Executable Statements ..
133 *
134  upper = lsame( uplo, 'U' )
135  IF (upper) THEN
136 *
137 * UPPER
138 * first swap
139 * - swap column I1 and I2 from I1 to I1-1
140  CALL dswap( i1-1, a(1,i1), 1, a(1,i2), 1 )
141 *
142 * second swap :
143 * - swap A(I1,I1) and A(I2,I2)
144 * - swap row I1 from I1+1 to I2-1 with col I2 from I1+1 to I2-1
145  tmp=a(i1,i1)
146  a(i1,i1)=a(i2,i2)
147  a(i2,i2)=tmp
148 *
149  DO i=1,i2-i1-1
150  tmp=a(i1,i1+i)
151  a(i1,i1+i)=a(i1+i,i2)
152  a(i1+i,i2)=tmp
153  END DO
154 *
155 * third swap
156 * - swap row I1 and I2 from I2+1 to N
157  DO i=i2+1,n
158  tmp=a(i1,i)
159  a(i1,i)=a(i2,i)
160  a(i2,i)=tmp
161  END DO
162 *
163  ELSE
164 *
165 * LOWER
166 * first swap
167 * - swap row I1 and I2 from I1 to I1-1
168  CALL dswap( i1-1, a(i1,1), lda, a(i2,1), lda )
169 *
170 * second swap :
171 * - swap A(I1,I1) and A(I2,I2)
172 * - swap col I1 from I1+1 to I2-1 with row I2 from I1+1 to I2-1
173  tmp=a(i1,i1)
174  a(i1,i1)=a(i2,i2)
175  a(i2,i2)=tmp
176 *
177  DO i=1,i2-i1-1
178  tmp=a(i1+i,i1)
179  a(i1+i,i1)=a(i2,i1+i)
180  a(i2,i1+i)=tmp
181  END DO
182 *
183 * third swap
184 * - swap col I1 and I2 from I2+1 to N
185  DO i=i2+1,n
186  tmp=a(i,i1)
187  a(i,i1)=a(i,i2)
188  a(i,i2)=tmp
189  END DO
190 *
191  ENDIF
192  END SUBROUTINE dsyswapr
193