60 lines
1.4 KiB
Fortran
60 lines
1.4 KiB
Fortran
recursive subroutine fpbacp(a,b,z,n,k,c,k1,nest)
|
|
implicit none
|
|
c subroutine fpbacp calculates the solution of the system of equations
|
|
c g * c = z with g a n x n upper triangular matrix of the form
|
|
c ! a ' !
|
|
c g = ! ' b !
|
|
c ! 0 ' !
|
|
c with b a n x k matrix and a a (n-k) x (n-k) upper triangular
|
|
c matrix of bandwidth k1.
|
|
c ..
|
|
c ..scalar arguments..
|
|
integer n,k,k1,nest
|
|
c ..array arguments..
|
|
real*8 a(nest,k1),b(nest,k),z(n),c(n)
|
|
c ..local scalars..
|
|
integer i,i1,j,l,l0,l1,n2
|
|
real*8 store
|
|
c ..
|
|
n2 = n-k
|
|
l = n
|
|
do 30 i=1,k
|
|
store = z(l)
|
|
j = k+2-i
|
|
if(i.eq.1) go to 20
|
|
l0 = l
|
|
do 10 l1=j,k
|
|
l0 = l0+1
|
|
store = store-c(l0)*b(l,l1)
|
|
10 continue
|
|
20 c(l) = store/b(l,j-1)
|
|
l = l-1
|
|
if(l.eq.0) go to 80
|
|
30 continue
|
|
do 50 i=1,n2
|
|
store = z(i)
|
|
l = n2
|
|
do 40 j=1,k
|
|
l = l+1
|
|
store = store-c(l)*b(i,j)
|
|
40 continue
|
|
c(i) = store
|
|
50 continue
|
|
i = n2
|
|
c(i) = c(i)/a(i,1)
|
|
if(i.eq.1) go to 80
|
|
do 70 j=2,n2
|
|
i = i-1
|
|
store = c(i)
|
|
i1 = k
|
|
if(j.le.k) i1=j-1
|
|
l = i
|
|
do 60 l0=1,i1
|
|
l = l+1
|
|
store = store-c(l)*a(i,l0+1)
|
|
60 continue
|
|
c(i) = store/a(i,1)
|
|
70 continue
|
|
80 return
|
|
end
|