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annotate libcruft/lapack/spttrs.f @ 7789:82be108cc558

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First attempt at single precision tyeps * * * corrections to qrupdate single precision routines * * * prefer demotion to single over promotion to double * * * Add single precision support to log2 function * * * Trivial PROJECT file update * * * Cache optimized hermitian/transpose methods * * * Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author David Bateman <dbateman@free.fr>
date Sun, 27 Apr 2008 22:34:17 +0200
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1 SUBROUTINE SPTTRS( N, NRHS, D, E, B, LDB, INFO )
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2 *
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3 * -- LAPACK routine (version 3.1) --
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4 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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5 * November 2006
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6 *
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7 * .. Scalar Arguments ..
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8 INTEGER INFO, LDB, N, NRHS
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9 * ..
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10 * .. Array Arguments ..
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11 REAL B( LDB, * ), D( * ), E( * )
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12 * ..
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13 *
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14 * Purpose
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15 * =======
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16 *
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17 * SPTTRS solves a tridiagonal system of the form
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18 * A * X = B
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19 * using the L*D*L' factorization of A computed by SPTTRF. D is a
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20 * diagonal matrix specified in the vector D, L is a unit bidiagonal
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21 * matrix whose subdiagonal is specified in the vector E, and X and B
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22 * are N by NRHS matrices.
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23 *
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24 * Arguments
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25 * =========
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26 *
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27 * N (input) INTEGER
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28 * The order of the tridiagonal matrix A. N >= 0.
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29 *
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30 * NRHS (input) INTEGER
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31 * The number of right hand sides, i.e., the number of columns
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32 * of the matrix B. NRHS >= 0.
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33 *
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34 * D (input) REAL array, dimension (N)
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35 * The n diagonal elements of the diagonal matrix D from the
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36 * L*D*L' factorization of A.
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37 *
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38 * E (input) REAL array, dimension (N-1)
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39 * The (n-1) subdiagonal elements of the unit bidiagonal factor
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40 * L from the L*D*L' factorization of A. E can also be regarded
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41 * as the superdiagonal of the unit bidiagonal factor U from the
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42 * factorization A = U'*D*U.
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43 *
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44 * B (input/output) REAL array, dimension (LDB,NRHS)
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45 * On entry, the right hand side vectors B for the system of
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46 * linear equations.
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47 * On exit, the solution vectors, X.
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48 *
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49 * LDB (input) INTEGER
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50 * The leading dimension of the array B. LDB >= max(1,N).
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51 *
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52 * INFO (output) INTEGER
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53 * = 0: successful exit
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54 * < 0: if INFO = -k, the k-th argument had an illegal value
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55 *
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56 * =====================================================================
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57 *
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58 * .. Local Scalars ..
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59 INTEGER J, JB, NB
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60 * ..
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61 * .. External Functions ..
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62 INTEGER ILAENV
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63 EXTERNAL ILAENV
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64 * ..
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65 * .. External Subroutines ..
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66 EXTERNAL SPTTS2, XERBLA
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67 * ..
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68 * .. Intrinsic Functions ..
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69 INTRINSIC MAX, MIN
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70 * ..
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71 * .. Executable Statements ..
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72 *
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73 * Test the input arguments.
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74 *
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75 INFO = 0
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76 IF( N.LT.0 ) THEN
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77 INFO = -1
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78 ELSE IF( NRHS.LT.0 ) THEN
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79 INFO = -2
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80 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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81 INFO = -6
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82 END IF
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83 IF( INFO.NE.0 ) THEN
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84 CALL XERBLA( 'SPTTRS', -INFO )
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85 RETURN
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86 END IF
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87 *
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88 * Quick return if possible
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89 *
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90 IF( N.EQ.0 .OR. NRHS.EQ.0 )
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91 $ RETURN
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92 *
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93 * Determine the number of right-hand sides to solve at a time.
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94 *
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95 IF( NRHS.EQ.1 ) THEN
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96 NB = 1
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97 ELSE
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98 NB = MAX( 1, ILAENV( 1, 'SPTTRS', ' ', N, NRHS, -1, -1 ) )
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99 END IF
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100 *
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101 IF( NB.GE.NRHS ) THEN
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102 CALL SPTTS2( N, NRHS, D, E, B, LDB )
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103 ELSE
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104 DO 10 J = 1, NRHS, NB
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105 JB = MIN( NRHS-J+1, NB )
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106 CALL SPTTS2( N, JB, D, E, B( 1, J ), LDB )
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107 10 CONTINUE
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108 END IF
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109 *
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110 RETURN
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111 *
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112 * End of SPTTRS
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113 *
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114 END