ScaLAPACK 2.1  2.1 ScaLAPACK: Scalable Linear Algebra PACKage
zpttrsv.f
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1  SUBROUTINE zpttrsv( UPLO, TRANS, N, NRHS, D, E, B, LDB,
2  \$ INFO )
3 *
4 * -- ScaLAPACK auxiliary routine (version 2.0) --
5 * Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver
6 *
7 * Written by Andrew J. Cleary, University of Tennessee.
8 * November, 1996.
9 * Modified from ZPTTRS:
10 * -- LAPACK routine (preliminary version) --
11 * Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
12 * Courant Institute, Argonne National Lab, and Rice University
13 *
14 * .. Scalar Arguments ..
15  CHARACTER UPLO, TRANS
16  INTEGER INFO, LDB, N, NRHS
17 * ..
18 * .. Array Arguments ..
19  DOUBLE PRECISION D( * )
20  COMPLEX*16 B( LDB, * ), E( * )
21 * ..
22 *
23 * Purpose
24 * =======
25 *
26 * ZPTTRSV solves one of the triangular systems
27 * L * X = B, or L**H * X = B,
28 * U * X = B, or U**H * X = B,
29 * where L or U is the Cholesky factor of a Hermitian positive
30 * definite tridiagonal matrix A such that
31 * A = U**H*D*U or A = L*D*L**H (computed by ZPTTRF).
32 *
33 * Arguments
34 * =========
35 *
36 * UPLO (input) CHARACTER*1
37 * Specifies whether the superdiagonal or the subdiagonal
38 * of the tridiagonal matrix A is stored and the form of the
39 * factorization:
40 * = 'U': E is the superdiagonal of U, and A = U'*D*U;
41 * = 'L': E is the subdiagonal of L, and A = L*D*L'.
42 * (The two forms are equivalent if A is real.)
43 *
44 * TRANS (input) CHARACTER
45 * Specifies the form of the system of equations:
46 * = 'N': L * X = B (No transpose)
47 * = 'N': L * X = B (No transpose)
48 * = 'C': U**H * X = B (Conjugate transpose)
49 * = 'C': L**H * X = B (Conjugate transpose)
50 *
51 * N (input) INTEGER
52 * The order of the tridiagonal matrix A. N >= 0.
53 *
54 * NRHS (input) INTEGER
55 * The number of right hand sides, i.e., the number of columns
56 * of the matrix B. NRHS >= 0.
57 *
58 * D (input) REAL array, dimension (N)
59 * The n diagonal elements of the diagonal matrix D from the
60 * factorization computed by ZPTTRF.
61 *
62 * E (input) COMPLEX array, dimension (N-1)
63 * The (n-1) off-diagonal elements of the unit bidiagonal
64 * factor U or L from the factorization computed by ZPTTRF
65 * (see UPLO).
66 *
67 * B (input/output) COMPLEX array, dimension (LDB,NRHS)
68 * On entry, the right hand side matrix B.
69 * On exit, the solution matrix X.
70 *
71 * LDB (input) INTEGER
72 * The leading dimension of the array B. LDB >= max(1,N).
73 *
74 * INFO (output) INTEGER
75 * = 0: successful exit
76 * < 0: if INFO = -i, the i-th argument had an illegal value
77 *
78 * =====================================================================
79 *
80 * .. Local Scalars ..
81  LOGICAL NOTRAN, UPPER
82  INTEGER I, J
83 * ..
84 * .. External Functions ..
85  LOGICAL LSAME
86  EXTERNAL lsame
87 * ..
88 * .. External Subroutines ..
89  EXTERNAL xerbla
90 * ..
91 * .. Intrinsic Functions ..
92  INTRINSIC dconjg, max
93 * ..
94 * .. Executable Statements ..
95 *
96 * Test the input arguments.
97 *
98  info = 0
99  notran = lsame( trans, 'N' )
100  upper = lsame( uplo, 'U' )
101  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
102  info = -1
103  ELSE IF( .NOT.notran .AND. .NOT.
104  \$ lsame( trans, 'C' ) ) THEN
105  info = -2
106  ELSE IF( n.LT.0 ) THEN
107  info = -3
108  ELSE IF( nrhs.LT.0 ) THEN
109  info = -4
110  ELSE IF( ldb.LT.max( 1, n ) ) THEN
111  info = -8
112  END IF
113  IF( info.NE.0 ) THEN
114  CALL xerbla( 'ZPTTRS', -info )
115  RETURN
116  END IF
117 *
118 * Quick return if possible
119 *
120  IF( n.EQ.0 )
121  \$ RETURN
122 *
123  IF( upper ) THEN
124 *
125  IF( .NOT.notran ) THEN
126 *
127  DO 30 j = 1, nrhs
128 *
129 * Solve U**T (or H) * x = b.
130 *
131  DO 10 i = 2, n
132  b( i, j ) = b( i, j ) - b( i-1, j )*dconjg( e( i-1 ) )
133  10 CONTINUE
134  30 CONTINUE
135 *
136  ELSE
137 *
138  DO 35 j = 1, nrhs
139 *
140 * Solve U * x = b.
141 *
142  DO 20 i = n - 1, 1, -1
143  b( i, j ) = b( i, j ) - b( i+1, j )*e( i )
144  20 CONTINUE
145  35 CONTINUE
146  ENDIF
147 *
148  ELSE
149 *
150  IF( notran ) THEN
151 *
152  DO 60 j = 1, nrhs
153 *
154 * Solve L * x = b.
155 *
156  DO 40 i = 2, n
157  b( i, j ) = b( i, j ) - b( i-1, j )*e( i-1 )
158  40 CONTINUE
159  60 CONTINUE
160 *
161  ELSE
162 *
163  DO 65 j = 1, nrhs
164 *
165 * Solve L**H * x = b.
166 *
167  DO 50 i = n - 1, 1, -1
168  b( i, j ) = b( i, j ) -
169  \$ b( i+1, j )*dconjg( e( i ) )
170  50 CONTINUE
171  65 CONTINUE
172  ENDIF
173 *
174  END IF
175 *
176  RETURN
177 *
178 * End of ZPTTRS
179 *
180  END
zpttrsv
subroutine zpttrsv(UPLO, TRANS, N, NRHS, D, E, B, LDB, INFO)
Definition: zpttrsv.f:3
max
#define max(A, B)
Definition: pcgemr.c:180