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qrfac.c

/* qrfac.f -- translated by f2c (version 20030306).
   You must link the resulting object file with the libraries:
      -lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Table of constant values */

static integer c__1 = 1;

/* Subroutine */ int qrfac_(integer *m, integer *n, doublereal *a, integer *
      lda, logical *pivot, integer *ipvt, integer *lipvt, doublereal *rdiag,
       doublereal *acnorm, doublereal *wa)
{
    /* Initialized data */

    static doublereal one = 1.;
    static doublereal p05 = .05;
    static doublereal zero = 0.;

    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3;
    doublereal d__1, d__2, d__3;

    /* Builtin functions */
    double sqrt(doublereal);

    /* Local variables */
    static integer i__, j, k, jp1;
    static doublereal sum;
    static integer kmax;
    static doublereal temp;
    static integer minmn;
    extern doublereal enorm_(integer *, doublereal *);
    static doublereal epsmch;
    extern doublereal dpmpar_(integer *);
    static doublereal ajnorm;

/*     ********** */

/*     subroutine qrfac */

/*     this subroutine uses householder transformations with column */
/*     pivoting (optional) to compute a qr factorization of the */
/*     m by n matrix a. that is, qrfac determines an orthogonal */
/*     matrix q, a permutation matrix p, and an upper trapezoidal */
/*     matrix r with diagonal elements of nonincreasing magnitude, */
/*     such that a*p = q*r. the householder transformation for */
/*     column k, k = 1,2,...,min(m,n), is of the form */

/*                           t */
/*           i - (1/u(k))*u*u */

/*     where u has zeros in the first k-1 positions. the form of */
/*     this transformation and the method of pivoting first */
/*     appeared in the corresponding linpack subroutine. */

/*     the subroutine statement is */

/*       subroutine qrfac(m,n,a,lda,pivot,ipvt,lipvt,rdiag,acnorm,wa) */

/*     where */

/*       m is a positive integer input variable set to the number */
/*         of rows of a. */

/*       n is a positive integer input variable set to the number */
/*         of columns of a. */

/*       a is an m by n array. on input a contains the matrix for */
/*         which the qr factorization is to be computed. on output */
/*         the strict upper trapezoidal part of a contains the strict */
/*         upper trapezoidal part of r, and the lower trapezoidal */
/*         part of a contains a factored form of q (the non-trivial */
/*         elements of the u vectors described above). */

/*       lda is a positive integer input variable not less than m */
/*         which specifies the leading dimension of the array a. */

/*       pivot is a logical input variable. if pivot is set true, */
/*         then column pivoting is enforced. if pivot is set false, */
/*         then no column pivoting is done. */

/*       ipvt is an integer output array of length lipvt. ipvt */
/*         defines the permutation matrix p such that a*p = q*r. */
/*         column j of p is column ipvt(j) of the identity matrix. */
/*         if pivot is false, ipvt is not referenced. */

/*       lipvt is a positive integer input variable. if pivot is false, */
/*         then lipvt may be as small as 1. if pivot is true, then */
/*         lipvt must be at least n. */

/*       rdiag is an output array of length n which contains the */
/*         diagonal elements of r. */

/*       acnorm is an output array of length n which contains the */
/*         norms of the corresponding columns of the input matrix a. */
/*         if this information is not needed, then acnorm can coincide */
/*         with rdiag. */

/*       wa is a work array of length n. if pivot is false, then wa */
/*         can coincide with rdiag. */

/*     subprograms called */

/*       minpack-supplied ... dpmpar,enorm */

/*       fortran-supplied ... dmax1,dsqrt,min0 */

/*     argonne national laboratory. minpack project. march 1980. */
/*     burton s. garbow, kenneth e. hillstrom, jorge j. more */

/*     ********** */
    /* Parameter adjustments */
    --wa;
    --acnorm;
    --rdiag;
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --ipvt;

    /* Function Body */

/*     epsmch is the machine precision. */

    epsmch = dpmpar_(&c__1);

/*     compute the initial column norms and initialize several arrays. */

    i__1 = *n;
    for (j = 1; j <= i__1; ++j) {
      acnorm[j] = enorm_(m, &a[j * a_dim1 + 1]);
      rdiag[j] = acnorm[j];
      wa[j] = rdiag[j];
      if (*pivot) {
          ipvt[j] = j;
      }
/* L10: */
    }

/*     reduce a to r with householder transformations. */

    minmn = min(*m,*n);
    i__1 = minmn;
    for (j = 1; j <= i__1; ++j) {
      if (! (*pivot)) {
          goto L40;
      }

/*        bring the column of largest norm into the pivot position. */

      kmax = j;
      i__2 = *n;
      for (k = j; k <= i__2; ++k) {
          if (rdiag[k] > rdiag[kmax]) {
            kmax = k;
          }
/* L20: */
      }
      if (kmax == j) {
          goto L40;
      }
      i__2 = *m;
      for (i__ = 1; i__ <= i__2; ++i__) {
          temp = a[i__ + j * a_dim1];
          a[i__ + j * a_dim1] = a[i__ + kmax * a_dim1];
          a[i__ + kmax * a_dim1] = temp;
/* L30: */
      }
      rdiag[kmax] = rdiag[j];
      wa[kmax] = wa[j];
      k = ipvt[j];
      ipvt[j] = ipvt[kmax];
      ipvt[kmax] = k;
L40:

/*        compute the householder transformation to reduce the */
/*        j-th column of a to a multiple of the j-th unit vector. */

      i__2 = *m - j + 1;
      ajnorm = enorm_(&i__2, &a[j + j * a_dim1]);
      if (ajnorm == zero) {
          goto L100;
      }
      if (a[j + j * a_dim1] < zero) {
          ajnorm = -ajnorm;
      }
      i__2 = *m;
      for (i__ = j; i__ <= i__2; ++i__) {
          a[i__ + j * a_dim1] /= ajnorm;
/* L50: */
      }
      a[j + j * a_dim1] += one;

/*        apply the transformation to the remaining columns */
/*        and update the norms. */

      jp1 = j + 1;
      if (*n < jp1) {
          goto L100;
      }
      i__2 = *n;
      for (k = jp1; k <= i__2; ++k) {
          sum = zero;
          i__3 = *m;
          for (i__ = j; i__ <= i__3; ++i__) {
            sum += a[i__ + j * a_dim1] * a[i__ + k * a_dim1];
/* L60: */
          }
          temp = sum / a[j + j * a_dim1];
          i__3 = *m;
          for (i__ = j; i__ <= i__3; ++i__) {
            a[i__ + k * a_dim1] -= temp * a[i__ + j * a_dim1];
/* L70: */
          }
          if (! (*pivot) || rdiag[k] == zero) {
            goto L80;
          }
          temp = a[j + k * a_dim1] / rdiag[k];
/* Computing MAX */
/* Computing 2nd power */
          d__3 = temp;
          d__1 = zero, d__2 = one - d__3 * d__3;
          rdiag[k] *= sqrt((max(d__1,d__2)));
/* Computing 2nd power */
          d__1 = rdiag[k] / wa[k];
          if (p05 * (d__1 * d__1) > epsmch) {
            goto L80;
          }
          i__3 = *m - j;
          rdiag[k] = enorm_(&i__3, &a[jp1 + k * a_dim1]);
          wa[k] = rdiag[k];
L80:
/* L90: */
          ;
      }
L100:
      rdiag[j] = -ajnorm;
/* L110: */
    }
    return 0;

/*     last card of subroutine qrfac. */

} /* qrfac_ */


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