cgtt02.c
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00001 /* cgtt02.f -- translated by f2c (version 20061008).
00002    You must link the resulting object file with libf2c:
00003         on Microsoft Windows system, link with libf2c.lib;
00004         on Linux or Unix systems, link with .../path/to/libf2c.a -lm
00005         or, if you install libf2c.a in a standard place, with -lf2c -lm
00006         -- in that order, at the end of the command line, as in
00007                 cc *.o -lf2c -lm
00008         Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
00009 
00010                 http://www.netlib.org/f2c/libf2c.zip
00011 */
00012 
00013 #include "f2c.h"
00014 #include "blaswrap.h"
00015 
00016 /* Table of constant values */
00017 
00018 static real c_b6 = -1.f;
00019 static real c_b7 = 1.f;
00020 static integer c__1 = 1;
00021 
00022 /* Subroutine */ int cgtt02_(char *trans, integer *n, integer *nrhs, complex *
00023         dl, complex *d__, complex *du, complex *x, integer *ldx, complex *b, 
00024         integer *ldb, real *rwork, real *resid)
00025 {
00026     /* System generated locals */
00027     integer b_dim1, b_offset, x_dim1, x_offset, i__1;
00028     real r__1, r__2;
00029 
00030     /* Local variables */
00031     integer j;
00032     real eps;
00033     extern logical lsame_(char *, char *);
00034     real anorm, bnorm, xnorm;
00035     extern doublereal slamch_(char *), clangt_(char *, integer *, 
00036             complex *, complex *, complex *);
00037     extern /* Subroutine */ int clagtm_(char *, integer *, integer *, real *, 
00038             complex *, complex *, complex *, complex *, integer *, real *, 
00039             complex *, integer *);
00040     extern doublereal scasum_(integer *, complex *, integer *);
00041 
00042 
00043 /*  -- LAPACK test routine (version 3.1) -- */
00044 /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
00045 /*     November 2006 */
00046 
00047 /*     .. Scalar Arguments .. */
00048 /*     .. */
00049 /*     .. Array Arguments .. */
00050 /*     .. */
00051 
00052 /*  Purpose */
00053 /*  ======= */
00054 
00055 /*  CGTT02 computes the residual for the solution to a tridiagonal */
00056 /*  system of equations: */
00057 /*     RESID = norm(B - op(A)*X) / (norm(A) * norm(X) * EPS), */
00058 /*  where EPS is the machine epsilon. */
00059 
00060 /*  Arguments */
00061 /*  ========= */
00062 
00063 /*  TRANS   (input) CHARACTER */
00064 /*          Specifies the form of the residual. */
00065 /*          = 'N':  B - A * X     (No transpose) */
00066 /*          = 'T':  B - A**T * X  (Transpose) */
00067 /*          = 'C':  B - A**H * X  (Conjugate transpose) */
00068 
00069 /*  N       (input) INTEGTER */
00070 /*          The order of the matrix A.  N >= 0. */
00071 
00072 /*  NRHS    (input) INTEGER */
00073 /*          The number of right hand sides, i.e., the number of columns */
00074 /*          of the matrices B and X.  NRHS >= 0. */
00075 
00076 /*  DL      (input) COMPLEX array, dimension (N-1) */
00077 /*          The (n-1) sub-diagonal elements of A. */
00078 
00079 /*  D       (input) COMPLEX array, dimension (N) */
00080 /*          The diagonal elements of A. */
00081 
00082 /*  DU      (input) COMPLEX array, dimension (N-1) */
00083 /*          The (n-1) super-diagonal elements of A. */
00084 
00085 /*  X       (input) COMPLEX array, dimension (LDX,NRHS) */
00086 /*          The computed solution vectors X. */
00087 
00088 /*  LDX     (input) INTEGER */
00089 /*          The leading dimension of the array X.  LDX >= max(1,N). */
00090 
00091 /*  B       (input/output) COMPLEX array, dimension (LDB,NRHS) */
00092 /*          On entry, the right hand side vectors for the system of */
00093 /*          linear equations. */
00094 /*          On exit, B is overwritten with the difference B - op(A)*X. */
00095 
00096 /*  LDB     (input) INTEGER */
00097 /*          The leading dimension of the array B.  LDB >= max(1,N). */
00098 
00099 /*  RWORK   (workspace) REAL array, dimension (N) */
00100 
00101 /*  RESID   (output) REAL */
00102 /*          norm(B - op(A)*X) / (norm(A) * norm(X) * EPS) */
00103 
00104 /*  ===================================================================== */
00105 
00106 /*     .. Parameters .. */
00107 /*     .. */
00108 /*     .. Local Scalars .. */
00109 /*     .. */
00110 /*     .. External Functions .. */
00111 /*     .. */
00112 /*     .. External Subroutines .. */
00113 /*     .. */
00114 /*     .. Intrinsic Functions .. */
00115 /*     .. */
00116 /*     .. Executable Statements .. */
00117 
00118 /*     Quick exit if N = 0 or NRHS = 0 */
00119 
00120     /* Parameter adjustments */
00121     --dl;
00122     --d__;
00123     --du;
00124     x_dim1 = *ldx;
00125     x_offset = 1 + x_dim1;
00126     x -= x_offset;
00127     b_dim1 = *ldb;
00128     b_offset = 1 + b_dim1;
00129     b -= b_offset;
00130     --rwork;
00131 
00132     /* Function Body */
00133     *resid = 0.f;
00134     if (*n <= 0 || *nrhs == 0) {
00135         return 0;
00136     }
00137 
00138 /*     Compute the maximum over the number of right hand sides of */
00139 /*        norm(B - op(A)*X) / ( norm(A) * norm(X) * EPS ). */
00140 
00141     if (lsame_(trans, "N")) {
00142         anorm = clangt_("1", n, &dl[1], &d__[1], &du[1]);
00143     } else {
00144         anorm = clangt_("I", n, &dl[1], &d__[1], &du[1]);
00145     }
00146 
00147 /*     Exit with RESID = 1/EPS if ANORM = 0. */
00148 
00149     eps = slamch_("Epsilon");
00150     if (anorm <= 0.f) {
00151         *resid = 1.f / eps;
00152         return 0;
00153     }
00154 
00155 /*     Compute B - op(A)*X. */
00156 
00157     clagtm_(trans, n, nrhs, &c_b6, &dl[1], &d__[1], &du[1], &x[x_offset], ldx, 
00158              &c_b7, &b[b_offset], ldb);
00159 
00160     i__1 = *nrhs;
00161     for (j = 1; j <= i__1; ++j) {
00162         bnorm = scasum_(n, &b[j * b_dim1 + 1], &c__1);
00163         xnorm = scasum_(n, &x[j * x_dim1 + 1], &c__1);
00164         if (xnorm <= 0.f) {
00165             *resid = 1.f / eps;
00166         } else {
00167 /* Computing MAX */
00168             r__1 = *resid, r__2 = bnorm / anorm / xnorm / eps;
00169             *resid = dmax(r__1,r__2);
00170         }
00171 /* L10: */
00172     }
00173 
00174     return 0;
00175 
00176 /*     End of CGTT02 */
00177 
00178 } /* cgtt02_ */


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autogenerated on Sat Jun 8 2019 18:55:28