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1 SUBROUTINE DPTSV( 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 DOUBLE PRECISION 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 * DPTSV computes the solution to a real system of linear equations |
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18 * A*X = B, where A is an N-by-N symmetric positive definite tridiagonal |
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19 * matrix, and X and B are N-by-NRHS matrices. |
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20 * |
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21 * A is factored as A = L*D*L**T, and the factored form of A is then |
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22 * used to solve the system of equations. |
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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 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/output) DOUBLE PRECISION array, dimension (N) |
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35 * On entry, the n diagonal elements of the tridiagonal matrix |
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36 * A. On exit, the n diagonal elements of the diagonal matrix |
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37 * D from the factorization A = L*D*L**T. |
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38 * |
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39 * E (input/output) DOUBLE PRECISION array, dimension (N-1) |
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40 * On entry, the (n-1) subdiagonal elements of the tridiagonal |
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41 * matrix A. On exit, the (n-1) subdiagonal elements of the |
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42 * unit bidiagonal factor L from the L*D*L**T factorization of |
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43 * A. (E can also be regarded as the superdiagonal of the unit |
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44 * bidiagonal factor U from the U**T*D*U factorization of A.) |
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45 * |
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46 * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) |
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47 * On entry, the N-by-NRHS right hand side matrix B. |
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48 * On exit, if INFO = 0, the N-by-NRHS solution matrix X. |
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49 * |
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50 * LDB (input) INTEGER |
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51 * The leading dimension of the array B. LDB >= max(1,N). |
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52 * |
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53 * INFO (output) INTEGER |
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54 * = 0: successful exit |
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55 * < 0: if INFO = -i, the i-th argument had an illegal value |
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56 * > 0: if INFO = i, the leading minor of order i is not |
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57 * positive definite, and the solution has not been |
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58 * computed. The factorization has not been completed |
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59 * unless i = N. |
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60 * |
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61 * ===================================================================== |
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62 * |
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63 * .. External Subroutines .. |
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64 EXTERNAL DPTTRF, DPTTRS, XERBLA |
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65 * .. |
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66 * .. Intrinsic Functions .. |
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67 INTRINSIC MAX |
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68 * .. |
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69 * .. Executable Statements .. |
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70 * |
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71 * Test the input parameters. |
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72 * |
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73 INFO = 0 |
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74 IF( N.LT.0 ) THEN |
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75 INFO = -1 |
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76 ELSE IF( NRHS.LT.0 ) THEN |
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77 INFO = -2 |
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78 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN |
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79 INFO = -6 |
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80 END IF |
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81 IF( INFO.NE.0 ) THEN |
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82 CALL XERBLA( 'DPTSV ', -INFO ) |
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83 RETURN |
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84 END IF |
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85 * |
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86 * Compute the L*D*L' (or U'*D*U) factorization of A. |
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87 * |
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88 CALL DPTTRF( N, D, E, INFO ) |
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89 IF( INFO.EQ.0 ) THEN |
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90 * |
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91 * Solve the system A*X = B, overwriting B with X. |
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92 * |
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93 CALL DPTTRS( N, NRHS, D, E, B, LDB, INFO ) |
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94 END IF |
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95 RETURN |
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96 * |
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97 * End of DPTSV |
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98 * |
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99 END |
