Permalink
Find file
Fetching contributors…
Cannot retrieve contributors at this time
93 lines (92 sloc) 2.79 KB
subroutine r1mpyq(m,n,a,lda,v,w)
integer m,n,lda
double precision a(lda,n),v(n),w(n)
c **********
c
c subroutine r1mpyq
c
c given an m by n matrix a, this subroutine computes a*q where
c q is the product of 2*(n - 1) transformations
c
c gv(n-1)*...*gv(1)*gw(1)*...*gw(n-1)
c
c and gv(i), gw(i) are givens rotations in the (i,n) plane which
c eliminate elements in the i-th and n-th planes, respectively.
c q itself is not given, rather the information to recover the
c gv, gw rotations is supplied.
c
c the subroutine statement is
c
c subroutine r1mpyq(m,n,a,lda,v,w)
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 must contain the matrix
c to be postmultiplied by the orthogonal matrix q
c described above. on output a*q has replaced a.
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 v is an input array of length n. v(i) must contain the
c information necessary to recover the givens rotation gv(i)
c described above.
c
c w is an input array of length n. w(i) must contain the
c information necessary to recover the givens rotation gw(i)
c described above.
c
c subroutines called
c
c fortran-supplied ... dabs,dsqrt
c
c argonne national laboratory. minpack project. march 1980.
c burton s. garbow, kenneth e. hillstrom, jorge j. more
c
c **********
integer i,j,nmj,nm1
double precision cos,one,sin,temp
data one /1.0d0/
c
c apply the first set of givens rotations to a.
c
nm1 = n - 1
if (nm1 .lt. 1) go to 50
do 20 nmj = 1, nm1
j = n - nmj
if (dabs(v(j)) .gt. one) cos = one/v(j)
if (dabs(v(j)) .gt. one) sin = dsqrt(one-cos**2)
if (dabs(v(j)) .le. one) sin = v(j)
if (dabs(v(j)) .le. one) cos = dsqrt(one-sin**2)
do 10 i = 1, m
temp = cos*a(i,j) - sin*a(i,n)
a(i,n) = sin*a(i,j) + cos*a(i,n)
a(i,j) = temp
10 continue
20 continue
c
c apply the second set of givens rotations to a.
c
do 40 j = 1, nm1
if (dabs(w(j)) .gt. one) cos = one/w(j)
if (dabs(w(j)) .gt. one) sin = dsqrt(one-cos**2)
if (dabs(w(j)) .le. one) sin = w(j)
if (dabs(w(j)) .le. one) cos = dsqrt(one-sin**2)
do 30 i = 1, m
temp = cos*a(i,j) + sin*a(i,n)
a(i,n) = -sin*a(i,j) + cos*a(i,n)
a(i,j) = temp
30 continue
40 continue
50 continue
return
c
c last card of subroutine r1mpyq.
c
end