C FPLQ4     SOURCE    CHAT      05/01/13    00:07:37     5004           
      FUNCTION FPLQ4(A,Y,Z)
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8(A-H,O-Z)
      A2=A**2
      Y2=Y**2
      Z2=Z**2
      C1=SQRT(A2+Y2+Z2)
      APC1=A+C1
      C2=A2+Z2
      C3=SQRT(C2)
      IF(Z.NE.0.) THEN
        SINUS=(A*C1+C2)/(C3*APC1) 
      ELSE 
        SINUS=SIGN(1.D0,A)
      ENDIF
      FPLQ4=Y*LOG(APC1)-Y+A*LOG(Y+C1)
     &     -Z*ASIN(SINUS)
      RETURN
      END