C^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                
      SUBROUTINE GSTEPF 
C^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                
      IMPLICIT REAL(A-H,O-Y)                                          
      IMPLICIT COMPLEX(Z)                                            
      INCLUDE 'PACVPP' 
      DO 30 I=1,KG
      IF (IG1(I).LE.-1) IGF1(I)=IG1(I)+2*IFX-1                          
      IF (IG1(I).GE. 0) IGF1(I)=IG1(I)+1                                
      IF (IG2(I).LE.-1) IGF2(I)=IG2(I)+2*IFY-1                          
      IF (IG2(I).GE. 0) IGF2(I)=IG2(I)+1                                
      IF (IG3(I).LE.-1) IGF3(I)=IG3(I)+2*IFZ-1                          
      IF (IG3(I).GE. 0) IGF3(I)=IG3(I)+1                                
   30 CONTINUE 
C     --------------------TETRAHEDRON VOLUME-------------------------   
      FFF =    RLTV(1,1)*(RLTV(2,2)*RLTV(3,3)-RLTV(3,2)*RLTV(2,3))
     &      +  RLTV(2,1)*(RLTV(3,2)*RLTV(1,3)-RLTV(1,2)*RLTV(3,3))      
     &      +  RLTV(3,1)*(RLTV(1,2)*RLTV(2,3)-RLTV(2,2)*RLTV(1,3)) 
      RVOL = ABS(FFF)                                                   
      DO 1000  K=1,KNZ2                                                 
      DO 1000  J=1,KNY2                                                 
      DO 1000  I=1,KNX2                                                 
      IGPO(I,J,K) = 0                                                   
 1000 CONTINUE                                                          
C     CALCULATION OF POINTER IGPO                                       
      DO 1100 I=1,KG                                                    
      IGPO(IG1(I)+KX1,IG2(I)+KY1,IG3(I)+KZ1)= I                         
 1100 CONTINUE                                                          
      RETURN                                                            
      END