ScaLAPACK 2.1  2.1 ScaLAPACK: Scalable Linear Algebra PACKage
dpttrsv.f
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1  SUBROUTINE dpttrsv( 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 DPTTRS:
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 TRANS
16  INTEGER INFO, LDB, N, NRHS
17 * ..
18 * .. Array Arguments ..
19  DOUBLE PRECISION D( * )
20  DOUBLE PRECISION B( LDB, * ), E( * )
21 * ..
22 *
23 * Purpose
24 * =======
25 *
26 * DPTTRSV solves one of the triangular systems
27 * L**T* X = B, or L * X = B,
28 * where L is the Cholesky factor of a Hermitian positive
29 * definite tridiagonal matrix A such that
30 * A = L*D*L**H (computed by DPTTRF).
31 *
32 * Arguments
33 * =========
34 *
35 * TRANS (input) CHARACTER
36 * Specifies the form of the system of equations:
37 * = 'N': L * X = B (No transpose)
38 * = 'T': L**T * X = B (Transpose)
39 *
40 * N (input) INTEGER
41 * The order of the tridiagonal matrix A. N >= 0.
42 *
43 * NRHS (input) INTEGER
44 * The number of right hand sides, i.e., the number of columns
45 * of the matrix B. NRHS >= 0.
46 *
47 * D (input) REAL array, dimension (N)
48 * The n diagonal elements of the diagonal matrix D from the
49 * factorization computed by DPTTRF.
50 *
51 * E (input) COMPLEX array, dimension (N-1)
52 * The (n-1) off-diagonal elements of the unit bidiagonal
53 * factor U or L from the factorization computed by DPTTRF
54 * (see UPLO).
55 *
56 * B (input/output) COMPLEX array, dimension (LDB,NRHS)
57 * On entry, the right hand side matrix B.
58 * On exit, the solution matrix X.
59 *
60 * LDB (input) INTEGER
61 * The leading dimension of the array B. LDB >= max(1,N).
62 *
63 * INFO (output) INTEGER
64 * = 0: successful exit
65 * < 0: if INFO = -i, the i-th argument had an illegal value
66 *
67 * =====================================================================
68 *
69 * .. Local Scalars ..
70  LOGICAL NOTRAN
71  INTEGER I, J
72 * ..
73 * .. External Functions ..
74  LOGICAL LSAME
75  EXTERNAL lsame
76 * ..
77 * .. External Subroutines ..
78  EXTERNAL xerbla
79 * ..
80 * .. Intrinsic Functions ..
81  INTRINSIC max
82 * ..
83 * .. Executable Statements ..
84 *
85 * Test the input arguments.
86 *
87  info = 0
88  notran = lsame( trans, 'N' )
89  IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) ) THEN
90  info = -1
91  ELSE IF( n.LT.0 ) THEN
92  info = -2
93  ELSE IF( nrhs.LT.0 ) THEN
94  info = -3
95  ELSE IF( ldb.LT.max( 1, n ) ) THEN
96  info = -7
97  END IF
98  IF( info.NE.0 ) THEN
99  CALL xerbla( 'DPTTRS', -info )
100  RETURN
101  END IF
102 *
103 * Quick return if possible
104 *
105  IF( n.EQ.0 )
106  \$ RETURN
107  IF( notran ) THEN
108 *
109  DO 60 j = 1, nrhs
110 *
111 * Solve L * x = b.
112 *
113  DO 40 i = 2, n
114  b( i, j ) = b( i, j ) - b( i-1, j )*e( i-1 )
115  40 CONTINUE
116  60 CONTINUE
117 *
118  ELSE
119 *
120  DO 65 j = 1, nrhs
121 *
122 * Solve L**H * x = b.
123 *
124  DO 50 i = n - 1, 1, -1
125  b( i, j ) = b( i, j ) -
126  \$ b( i+1, j )*( e( i ) )
127  50 CONTINUE
128  65 CONTINUE
129  ENDIF
130 *
131  RETURN
132 *
133 * End of DPTTRS
134 *
135  END
max
#define max(A, B)
Definition: pcgemr.c:180
dpttrsv
subroutine dpttrsv(TRANS, N, NRHS, D, E, B, LDB, INFO)
Definition: dpttrsv.f:3