C
C $Id: bndang.F,v 1.2 1998/07/16 16:39:25 jjv5 Exp arjan $
C
C------------------------------------------------------------------------
      SUBROUTINE BNDANG(XYZ,I,IA,IB,ANGLE)
C
C     COMPUTES THE ANGLE IN RADIANS FORMED BY ATOMS I-IA-IB.  RETURNED
C     IN ANGLE.
C
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      DIMENSION XYZ(3,*)
C
C     FORM THE BOND VECTORS WITH VERTEX IA.
C
      X1 = XYZ(1,I) - XYZ(1,IA)
      Y1 = XYZ(2,I) - XYZ(2,IA)
      Z1 = XYZ(3,I) - XYZ(3,IA)
      X2 = XYZ(1,IB) - XYZ(1,IA)
      Y2 = XYZ(2,IB) - XYZ(2,IA)
      Z2 = XYZ(3,IB) - XYZ(3,IA)
      VNORM1 = DSQRT(X1*X1 + Y1*Y1 + Z1*Z1)
      VNORM2 = DSQRT(X2*X2 + Y2*Y2 + Z2*Z2)
      COSINE = (X1*X2 + Y1*Y2 + Z1*Z2)/(VNORM1*VNORM2)
      IF(ABS(COSINE).GT.1.0D0) COSINE = SIGN(1.0D0,COSINE)
      ANGLE = ACOS(COSINE)
      RETURN
      END