pybksb.f

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C*********************************************************************
 
C...PYBKSB
C...Auxiliary to PYSIGH, for technicolor corrections to QCD 2 -> 2
C...processes.
 
      SUBROUTINE pybksb(A,N,NP,INDX,B)
      IMPLICIT NONE
      INTEGER n,np,indx(n)
      COMPLEX*16 a(np,np),b(n)
      INTEGER i,ii,j,ll
      COMPLEX*16 sum
 
      ii=0
      DO 110 i=1,n
        ll=indx(i)
        sum=b(ll)
        b(ll)=b(i)
        IF (ii.NE.0)THEN
          DO 100 j=ii,i-1
            sum=sum-a(i,j)*b(j)
  100     CONTINUE
        ELSE IF (abs(sum).NE.0d0) THEN
          ii=i
        ENDIF
        b(i)=sum
  110 CONTINUE
      DO 130 i=n,1,-1
        sum=b(i)
        DO 120 j=i+1,n
          sum=sum-a(i,j)*b(j)
  120   CONTINUE
        b(i)=sum/a(i,i)
  130 CONTINUE
      RETURN
      END