#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int clarfg_(integer *n, complex *alpha, complex *x, integer * incx, complex *tau) { /* -- LAPACK auxiliary routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= CLARFG generates a complex elementary reflector H of order n, such that H' * ( alpha ) = ( beta ), H' * H = I. ( x ) ( 0 ) where alpha and beta are scalars, with beta real, and x is an (n-1)-element complex vector. H is represented in the form H = I - tau * ( 1 ) * ( 1 v' ) , ( v ) where tau is a complex scalar and v is a complex (n-1)-element vector. Note that H is not hermitian. If the elements of x are all zero and alpha is real, then tau = 0 and H is taken to be the unit matrix. Otherwise 1 <= real(tau) <= 2 and abs(tau-1) <= 1 . Arguments ========= N (input) INTEGER The order of the elementary reflector. ALPHA (input/output) COMPLEX On entry, the value alpha. On exit, it is overwritten with the value beta. X (input/output) COMPLEX array, dimension (1+(N-2)*abs(INCX)) On entry, the vector x. On exit, it is overwritten with the vector v. INCX (input) INTEGER The increment between elements of X. INCX > 0. TAU (output) COMPLEX The value tau. ===================================================================== Parameter adjustments */ /* Table of constant values */ static complex c_b5 = {1.f,0.f}; /* System generated locals */ integer i__1; real r__1, r__2; complex q__1, q__2; /* Builtin functions */ double r_imag(complex *), r_sign(real *, real *); /* Local variables */ static integer j, knt; static real beta; extern /* Subroutine */ int cscal_(integer *, complex *, complex *, integer *); static real alphi, alphr, xnorm; extern doublereal scnrm2_(integer *, complex *, integer *), slapy3_(real * , real *, real *); extern /* Complex */ VOID cladiv_(complex *, complex *, complex *); extern doublereal slamch_(char *); extern /* Subroutine */ int csscal_(integer *, real *, complex *, integer *); static real safmin, rsafmn; --x; /* Function Body */ if (*n <= 0) { tau->r = 0.f, tau->i = 0.f; return 0; } i__1 = *n - 1; xnorm = scnrm2_(&i__1, &x[1], incx); alphr = alpha->r; alphi = r_imag(alpha); if (xnorm == 0.f && alphi == 0.f) { /* H = I */ tau->r = 0.f, tau->i = 0.f; } else { /* general case */ r__1 = slapy3_(&alphr, &alphi, &xnorm); beta = -r_sign(&r__1, &alphr); safmin = slamch_("S") / slamch_("E"); rsafmn = 1.f / safmin; if (dabs(beta) < safmin) { /* XNORM, BETA may be inaccurate; scale X and recompute them */ knt = 0; L10: ++knt; i__1 = *n - 1; csscal_(&i__1, &rsafmn, &x[1], incx); beta *= rsafmn; alphi *= rsafmn; alphr *= rsafmn; if (dabs(beta) < safmin) { goto L10; } /* New BETA is at most 1, at least SAFMIN */ i__1 = *n - 1; xnorm = scnrm2_(&i__1, &x[1], incx); q__1.r = alphr, q__1.i = alphi; alpha->r = q__1.r, alpha->i = q__1.i; r__1 = slapy3_(&alphr, &alphi, &xnorm); beta = -r_sign(&r__1, &alphr); r__1 = (beta - alphr) / beta; r__2 = -alphi / beta; q__1.r = r__1, q__1.i = r__2; tau->r = q__1.r, tau->i = q__1.i; q__2.r = alpha->r - beta, q__2.i = alpha->i; cladiv_(&q__1, &c_b5, &q__2); alpha->r = q__1.r, alpha->i = q__1.i; i__1 = *n - 1; cscal_(&i__1, alpha, &x[1], incx); /* If ALPHA is subnormal, it may lose relative accuracy */ alpha->r = beta, alpha->i = 0.f; i__1 = knt; for (j = 1; j <= i__1; ++j) { q__1.r = safmin * alpha->r, q__1.i = safmin * alpha->i; alpha->r = q__1.r, alpha->i = q__1.i; /* L20: */ } } else { r__1 = (beta - alphr) / beta; r__2 = -alphi / beta; q__1.r = r__1, q__1.i = r__2; tau->r = q__1.r, tau->i = q__1.i; q__2.r = alpha->r - beta, q__2.i = alpha->i; cladiv_(&q__1, &c_b5, &q__2); alpha->r = q__1.r, alpha->i = q__1.i; i__1 = *n - 1; cscal_(&i__1, alpha, &x[1], incx); alpha->r = beta, alpha->i = 0.f; } } return 0; /* End of CLARFG */ } /* clarfg_ */