Annotation of rpl/lapack/lapack/ztbtrs.f, revision 1.4
1.1 bertrand 1: SUBROUTINE ZTBTRS( UPLO, TRANS, DIAG, N, KD, NRHS, AB, LDAB, B,
2: $ LDB, INFO )
3: *
4: * -- LAPACK routine (version 3.2) --
5: * -- LAPACK is a software package provided by Univ. of Tennessee, --
6: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
7: * November 2006
8: *
9: * .. Scalar Arguments ..
10: CHARACTER DIAG, TRANS, UPLO
11: INTEGER INFO, KD, LDAB, LDB, N, NRHS
12: * ..
13: * .. Array Arguments ..
14: COMPLEX*16 AB( LDAB, * ), B( LDB, * )
15: * ..
16: *
17: * Purpose
18: * =======
19: *
20: * ZTBTRS solves a triangular system of the form
21: *
22: * A * X = B, A**T * X = B, or A**H * X = B,
23: *
24: * where A is a triangular band matrix of order N, and B is an
25: * N-by-NRHS matrix. A check is made to verify that A is nonsingular.
26: *
27: * Arguments
28: * =========
29: *
30: * UPLO (input) CHARACTER*1
31: * = 'U': A is upper triangular;
32: * = 'L': A is lower triangular.
33: *
34: * TRANS (input) CHARACTER*1
35: * Specifies the form of the system of equations:
36: * = 'N': A * X = B (No transpose)
37: * = 'T': A**T * X = B (Transpose)
38: * = 'C': A**H * X = B (Conjugate transpose)
39: *
40: * DIAG (input) CHARACTER*1
41: * = 'N': A is non-unit triangular;
42: * = 'U': A is unit triangular.
43: *
44: * N (input) INTEGER
45: * The order of the matrix A. N >= 0.
46: *
47: * KD (input) INTEGER
48: * The number of superdiagonals or subdiagonals of the
49: * triangular band matrix A. KD >= 0.
50: *
51: * NRHS (input) INTEGER
52: * The number of right hand sides, i.e., the number of columns
53: * of the matrix B. NRHS >= 0.
54: *
55: * AB (input) COMPLEX*16 array, dimension (LDAB,N)
56: * The upper or lower triangular band matrix A, stored in the
57: * first kd+1 rows of AB. The j-th column of A is stored
58: * in the j-th column of the array AB as follows:
59: * if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
60: * if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd).
61: * If DIAG = 'U', the diagonal elements of A are not referenced
62: * and are assumed to be 1.
63: *
64: * LDAB (input) INTEGER
65: * The leading dimension of the array AB. LDAB >= KD+1.
66: *
67: * B (input/output) COMPLEX*16 array, dimension (LDB,NRHS)
68: * On entry, the right hand side matrix B.
69: * On exit, if INFO = 0, 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: * > 0: if INFO = i, the i-th diagonal element of A is zero,
78: * indicating that the matrix is singular and the
79: * solutions X have not been computed.
80: *
81: * =====================================================================
82: *
83: * .. Parameters ..
84: COMPLEX*16 ZERO
85: PARAMETER ( ZERO = ( 0.0D+0, 0.0D+0 ) )
86: * ..
87: * .. Local Scalars ..
88: LOGICAL NOUNIT, UPPER
89: INTEGER J
90: * ..
91: * .. External Functions ..
92: LOGICAL LSAME
93: EXTERNAL LSAME
94: * ..
95: * .. External Subroutines ..
96: EXTERNAL XERBLA, ZTBSV
97: * ..
98: * .. Intrinsic Functions ..
99: INTRINSIC MAX
100: * ..
101: * .. Executable Statements ..
102: *
103: * Test the input parameters.
104: *
105: INFO = 0
106: NOUNIT = LSAME( DIAG, 'N' )
107: UPPER = LSAME( UPLO, 'U' )
108: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
109: INFO = -1
110: ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
111: $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
112: INFO = -2
113: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
114: INFO = -3
115: ELSE IF( N.LT.0 ) THEN
116: INFO = -4
117: ELSE IF( KD.LT.0 ) THEN
118: INFO = -5
119: ELSE IF( NRHS.LT.0 ) THEN
120: INFO = -6
121: ELSE IF( LDAB.LT.KD+1 ) THEN
122: INFO = -8
123: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
124: INFO = -10
125: END IF
126: IF( INFO.NE.0 ) THEN
127: CALL XERBLA( 'ZTBTRS', -INFO )
128: RETURN
129: END IF
130: *
131: * Quick return if possible
132: *
133: IF( N.EQ.0 )
134: $ RETURN
135: *
136: * Check for singularity.
137: *
138: IF( NOUNIT ) THEN
139: IF( UPPER ) THEN
140: DO 10 INFO = 1, N
141: IF( AB( KD+1, INFO ).EQ.ZERO )
142: $ RETURN
143: 10 CONTINUE
144: ELSE
145: DO 20 INFO = 1, N
146: IF( AB( 1, INFO ).EQ.ZERO )
147: $ RETURN
148: 20 CONTINUE
149: END IF
150: END IF
151: INFO = 0
152: *
153: * Solve A * X = B, A**T * X = B, or A**H * X = B.
154: *
155: DO 30 J = 1, NRHS
156: CALL ZTBSV( UPLO, TRANS, DIAG, N, KD, AB, LDAB, B( 1, J ), 1 )
157: 30 CONTINUE
158: *
159: RETURN
160: *
161: * End of ZTBTRS
162: *
163: END
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