c***********************************************************************
LOGICAL FUNCTION HALFSPACE(A,B,C,D,X,Y,Z,TOLHS)
c#@# KKRtags: VORONOI geometry
c Given a plane A*x+B*y+C*z=D, and a point (X,Y,Z) in space, this
c func takes the value TRUE if (X,Y,Z) lies in the half-space
c defined by the plane and the origin (0,0,0) (including the plane
c itself). Else, the value FALSE is returned.
c
c The criterion used is that the inner product of the vector (X,Y,Z)
c with the vector d connecting the origin to the plane vertically be
c less than or equal to d**2: (d_x,d_y,d_z)*(X,Y,Z) =< d**2.
c
c Input:
REAL*8 A,B,C,D,X,Y,Z,TEST,D1,D2,TOLHS
IF (DABS(A)+DABS(B)+DABS(C).LT.1.D-80)
& STOP 'HALFSPACE: A,B,C too small.'
HALFSPACE = .FALSE.
! IF (D*(A*X+B*Y+C*Z).LE.D*D) HALFSPACE = .TRUE.
IF (D*(A*X+B*Y+C*Z)-D*D.LT.TOLHS) HALFSPACE = .TRUE.
c (re-checked 31May2008 FM)
RETURN
END
