subroutine qrfac(m,n,a,lda,pivot,ipvt,lipvt,rdiag,acnorm,wa) integer m,n,lda,lipvt integer ipvt(lipvt) logical pivot real a(lda,n),rdiag(n),acnorm(n),wa(n) c ********** c c subroutine qrfac c c this subroutine uses householder transformations with column c pivoting (optional) to compute a qr factorization of the c m by n matrix a. that is, qrfac determines an orthogonal c matrix q, a permutation matrix p, and an upper trapezoidal c matrix r with diagonal elements of nonincreasing magnitude, c such that a*p = q*r. the householder transformation for c column k, k = 1,2,...,min(m,n), is of the form c c t c i - (1/u(k))*u*u c c where u has zeros in the first k-1 positions. the form of c this transformation and the method of pivoting first c appeared in the corresponding linpack subroutine. c c the subroutine statement is c c subroutine qrfac(m,n,a,lda,pivot,ipvt,lipvt,rdiag,acnorm,wa) c c where c c m is a positive integer input variable set to the number c of rows of a. c c n is a positive integer input variable set to the number c of columns of a. c c a is an m by n array. on input a contains the matrix for c which the qr factorization is to be computed. on output c the strict upper trapezoidal part of a contains the strict c upper trapezoidal part of r, and the lower trapezoidal c part of a contains a factored form of q (the non-trivial c elements of the u vectors described above). c c lda is a positive integer input variable not less than m c which specifies the leading dimension of the array a. c c pivot is a logical input variable. if pivot is set true, c then column pivoting is enforced. if pivot is set false, c then no column pivoting is done. c c ipvt is an integer output array of length lipvt. ipvt c defines the permutation matrix p such that a*p = q*r. c column j of p is column ipvt(j) of the identity matrix. c if pivot is false, ipvt is not referenced. c c lipvt is a positive integer input variable. if pivot is false, c then lipvt may be as small as 1. if pivot is true, then c lipvt must be at least n. c c rdiag is an output array of length n which contains the c diagonal elements of r. c c acnorm is an output array of length n which contains the c norms of the corresponding columns of the input matrix a. c if this information is not needed, then acnorm can coincide c with rdiag. c c wa is a work array of length n. if pivot is false, then wa c can coincide with rdiag. c c subprograms called c c minpack-supplied ... spmpar,enorm c c fortran-supplied ... amax1,sqrt,min0 c c argonne national laboratory. minpack project. march 1980. c burton s. garbow, kenneth e. hillstrom, jorge j. more c c ********** integer i,j,jp1,k,kmax,minmn real ajnorm,epsmch,one,p05,sum,temp,zero real spmpar,enorm data one,p05,zero /1.0e0,5.0e-2,0.0e0/ c c epsmch is the machine precision. c epsmch = spmpar(1) c c compute the initial column norms and initialize several arrays. c do 10 j = 1, n acnorm(j) = enorm(m,a(1,j)) rdiag(j) = acnorm(j) wa(j) = rdiag(j) if (pivot) ipvt(j) = j 10 continue c c reduce a to r with householder transformations. c minmn = min0(m,n) do 110 j = 1, minmn if (.not.pivot) go to 40 c c bring the column of largest norm into the pivot position. c kmax = j do 20 k = j, n if (rdiag(k) .gt. rdiag(kmax)) kmax = k 20 continue if (kmax .eq. j) go to 40 do 30 i = 1, m temp = a(i,j) a(i,j) = a(i,kmax) a(i,kmax) = temp 30 continue rdiag(kmax) = rdiag(j) wa(kmax) = wa(j) k = ipvt(j) ipvt(j) = ipvt(kmax) ipvt(kmax) = k 40 continue c c compute the householder transformation to reduce the c j-th column of a to a multiple of the j-th unit vector. c ajnorm = enorm(m-j+1,a(j,j)) if (ajnorm .eq. zero) go to 100 if (a(j,j) .lt. zero) ajnorm = -ajnorm do 50 i = j, m a(i,j) = a(i,j)/ajnorm 50 continue a(j,j) = a(j,j) + one c c apply the transformation to the remaining columns c and update the norms. c jp1 = j + 1 if (n .lt. jp1) go to 100 do 90 k = jp1, n sum = zero do 60 i = j, m sum = sum + a(i,j)*a(i,k) 60 continue temp = sum/a(j,j) do 70 i = j, m a(i,k) = a(i,k) - temp*a(i,j) 70 continue if (.not.pivot .or. rdiag(k) .eq. zero) go to 80 temp = a(j,k)/rdiag(k) rdiag(k) = rdiag(k)*sqrt(amax1(zero,one-temp**2)) if (p05*(rdiag(k)/wa(k))**2 .gt. epsmch) go to 80 rdiag(k) = enorm(m-j,a(jp1,k)) wa(k) = rdiag(k) 80 continue 90 continue 100 continue rdiag(j) = -ajnorm 110 continue return c c last card of subroutine qrfac. c end