+C Output from Public domain Ratfor, version 1.0
+ subroutine sinerp(abd,ld4,nk,p1ip,p2ip,ldnk,flag)
+c
+C Purpose : Computes Inner Products between columns of L^{-1}
+C where L = abd is a Banded Matrix with 3 subdiagonals
+
+C The algorithm works in two passes:
+C
+C Pass 1 computes (cj,ck) k=j,j-1,j-2,j-3 ; j=nk, .. 1
+C Pass 2 computes (cj,ck) k <= j-4 (If flag == 1 ).
+C
+C A refinement of Elden's trick is used.
+c Args
+ integer ld4,nk,ldnk,flag
+ DOUBLE precision abd(ld4,nk),p1ip(ld4,nk), p2ip(ldnk,nk)
+c Locals
+ integer i,j,k
+ DOUBLE precision wjm3(3),wjm2(2),wjm1(1),c0,c1,c2,c3
+c
+c unnecessary initialization of c1 c2 c3 to keep g77 -Wall happy
+c
+ c1 = 0.0d0
+ c2 = 0.0d0
+ c3 = 0.0d0
+C
+C Pass 1
+ wjm3(1)=0d0
+ wjm3(2)=0d0
+ wjm3(3)=0d0
+ wjm2(1)=0d0
+ wjm2(2)=0d0
+ wjm1(1)=0d0
+ do 100 i=1,nk
+ j=nk-i+1
+ c0 = 1d0/abd(4,j)
+ if(j.le.nk-3)then
+ c1 = abd(1,j+3)*c0
+ c2 = abd(2,j+2)*c0
+ c3 = abd(3,j+1)*c0
+ else if(j.eq.nk-2)then
+ c1 = 0d0
+ c2 = abd(2,j+2)*c0
+ c3 = abd(3,j+1)*c0
+ else if(j.eq.nk-1)then
+ c1 = 0d0
+ c2 = 0d0
+ c3 = abd(3,j+1)*c0
+ else if(j.eq.nk)then
+ c1 = 0d0
+ c2 = 0d0
+ c3 = 0d0
+ endif
+ p1ip(1,j) = 0d0- (c1*wjm3(1)+c2*wjm3(2)+c3*wjm3(3))
+ p1ip(2,j) = 0d0- (c1*wjm3(2)+c2*wjm2(1)+c3*wjm2(2))
+ p1ip(3,j) = 0d0- (c1*wjm3(3)+c2*wjm2(2)+c3*wjm1(1))
+ p1ip(4,j) = c0**2 + c1**2*wjm3(1) + 2d0*c1*c2*wjm3(2)+
+ & 2d0*c1*c3*wjm3(3) + c2**2*wjm2(1) + 2d0*c2*c3*wjm2(2) +
+ & c3**2*wjm1(1)
+ wjm3(1)=wjm2(1)
+ wjm3(2)=wjm2(2)
+ wjm3(3)=p1ip(2,j)
+ wjm2(1)=wjm1(1)
+ wjm2(2)=p1ip(3,j)
+ wjm1(1)=p1ip(4,j)
+ 100 continue
+
+ if(flag.ne.0)then
+
+C ____ Pass 2 _____
+
+C Compute p2ip
+ do 120 i=1,nk
+ j=nk-i+1
+C for(k=1;k<=4 & j+k-1<=nk;k=k+1) { p2ip(.) = .. }:
+ do 160 k=1,4
+ if(j+k-1 .gt. nk)goto 120
+ p2ip(j,j+k-1) = p1ip(5-k,j)
+ 160 continue
+ 120 continue
+
+ do 170 i=1,nk
+ j=nk-i+1
+c for(k=j-4;k>=1;k=k-1){
+ if(j-4 .ge. 1) then
+ do 210 k= j-4,1, -1
+ c0 = 1d0/abd(4,k)
+ c1 = abd(1,k+3)*c0
+ c2 = abd(2,k+2)*c0
+ c3 = abd(3,k+1)*c0
+ p2ip(k,j)= 0d0 - ( c1*p2ip(k+3,j) + c2*p2ip(k+2,j) +
+ & c3*p2ip(k+1,j) )
+ 210 continue
+ endif
+ 170 continue
+ endif
+ return
+ end
+