1: SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )
2: *
3: * -- LAPACK routine (version 3.2) --
4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
6: * November 2006
7: *
8: * .. Scalar Arguments ..
9: INTEGER INFO, LDB, N, NRHS
10: * ..
11: * .. Array Arguments ..
12: DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
13: * ..
14: *
15: * Purpose
16: * =======
17: *
18: * DPTSV computes the solution to a real system of linear equations
19: * A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
20: * matrix, and X and B are N-by-NRHS matrices.
21: *
22: * A is factored as A = L*D*L**T, and the factored form of A is then
23: * used to solve the system of equations.
24: *
25: * Arguments
26: * =========
27: *
28: * N (input) INTEGER
29: * The order of the matrix A. N >= 0.
30: *
31: * NRHS (input) INTEGER
32: * The number of right hand sides, i.e., the number of columns
33: * of the matrix B. NRHS >= 0.
34: *
35: * D (input/output) DOUBLE PRECISION array, dimension (N)
36: * On entry, the n diagonal elements of the tridiagonal matrix
37: * A. On exit, the n diagonal elements of the diagonal matrix
38: * D from the factorization A = L*D*L**T.
39: *
40: * E (input/output) DOUBLE PRECISION array, dimension (N-1)
41: * On entry, the (n-1) subdiagonal elements of the tridiagonal
42: * matrix A. On exit, the (n-1) subdiagonal elements of the
43: * unit bidiagonal factor L from the L*D*L**T factorization of
44: * A. (E can also be regarded as the superdiagonal of the unit
45: * bidiagonal factor U from the U**T*D*U factorization of A.)
46: *
47: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
48: * On entry, the N-by-NRHS right hand side matrix B.
49: * On exit, if INFO = 0, the N-by-NRHS solution matrix X.
50: *
51: * LDB (input) INTEGER
52: * The leading dimension of the array B. LDB >= max(1,N).
53: *
54: * INFO (output) INTEGER
55: * = 0: successful exit
56: * < 0: if INFO = -i, the i-th argument had an illegal value
57: * > 0: if INFO = i, the leading minor of order i is not
58: * positive definite, and the solution has not been
59: * computed. The factorization has not been completed
60: * unless i = N.
61: *
62: * =====================================================================
63: *
64: * .. External Subroutines ..
65: EXTERNAL DPTTRF, DPTTRS, XERBLA
66: * ..
67: * .. Intrinsic Functions ..
68: INTRINSIC MAX
69: * ..
70: * .. Executable Statements ..
71: *
72: * Test the input parameters.
73: *
74: INFO = 0
75: IF( N.LT.0 ) THEN
76: INFO = -1
77: ELSE IF( NRHS.LT.0 ) THEN
78: INFO = -2
79: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
80: INFO = -6
81: END IF
82: IF( INFO.NE.0 ) THEN
83: CALL XERBLA( 'DPTSV ', -INFO )
84: RETURN
85: END IF
86: *
87: * Compute the L*D*L' (or U'*D*U) factorization of A.
88: *
89: CALL DPTTRF( N, D, E, INFO )
90: IF( INFO.EQ.0 ) THEN
91: *
92: * Solve the system A*X = B, overwriting B with X.
93: *
94: CALL DPTTRS( N, NRHS, D, E, B, LDB, INFO )
95: END IF
96: RETURN
97: *
98: * End of DPTSV
99: *
100: END
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