swap.f File Reference

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Functions/Subroutines
logical function	swap (x1, y1, x2, y2, x3, y3, xp, yp)

Function/Subroutine Documentation

swap()

logical function swap	(	real*8	x1,
		real*8	y1,
		real*8	x2,
		real*8	y2,
		real*8	x3,
		real*8	y3,
		real*8	xp,
		real*8	yp
	)

!     
      implicit none
!     
      real*8 x1,y1,x2,y2,x3,y3,xp,yp,x13,y13,x23,y23,
     &     x1p,y1p,x2p,y2p,cosa,cosb,sina,sinb,c00000
!     
      logical swap
!     
      parameter(c00000=0.d0)
!     
      x13=x1-x3
      y13=y1-y3
      x23=x2-x3
      y23=y2-y3
      x1p=x1-xp
      y1p=y1-yp
      x2p=x2-xp
      y2p=y2-yp
      cosa=x13*x23+y13*y23
      cosb=x2p*x1p+y1p*y2p
      if((cosa.ge.c00000).and.(cosb.ge.c00000)) then
         swap=.false.
      elseif((cosa.lt.c00000).and.(cosb.lt.c00000)) then
         swap=.true.
      else
         sina=x13*y23-x23*y13
         sinb=x2p*y1p-x1p*y2p
         if((sina*cosb+sinb*cosa).lt.c00000) then
            swap=.true.
         else
            swap=.false.
         end if
      end if