C @(#)semilog.for	19.1 (ES0-DMD) 02/25/03 13:17:43
C===========================================================================
C Copyright (C) 1995 European Southern Observatory (ESO)
C
C This program is free software; you can redistribute it and/or 
C modify it under the terms of the GNU General Public License as 
C published by the Free Software Foundation; either version 2 of 
C the License, or (at your option) any later version.
C
C This program is distributed in the hope that it will be useful,
C but WITHOUT ANY WARRANTY; without even the implied warranty of
C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
C GNU General Public License for more details.
C
C You should have received a copy of the GNU General Public 
C License along with this program; if not, write to the Free 
C Software Foundation, Inc., 675 Massachusetss Ave, Cambridge, 
C MA 02139, USA.
C
C Corresponding concerning ESO-MIDAS should be addressed as follows:
C	Internet e-mail: midas@eso.org
C	Postal address: European Southern Observatory
C			Data Management Division 
C			Karl-Schwarzschild-Strasse 2
C			D 85748 Garching bei Muenchen 
C			GERMANY
C===========================================================================
C
      SUBROUTINE SEMILG(IND,X,NP,P,Y1,DY)                                      
C+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++                  
C.COPYRIGHT: Copyright (c) 1987 European Southern Observatory,                  
C                                         all rights reserved                   
C                                                                               
C.VERSION: 1.0  ESO-FORTRAN Conversion, AA  18:01 - 21 DEC 1987                 
C                                                                               
C.LANGUAGE: F77+ESOext                                                          
C                                                                               
C.AUTHOR: J.D.PONZ                                                              
C                                                                               
C--------------------------------------------------------------                 
C                                                                               
C SEMI-LOGISTIC DISTRIBUTION                                                    
C      IMPLICIT NONE                                                            
C                                                                               
C Y1 = 2.*P(1)/(1.+EXP(LN(3)*ABS(X-P(2))/P(3)))                                 
C                                                                               
      INTEGER IND,NP
      DOUBLE PRECISION Y1,P(NP),DY(NP),A,B,C,D,E,F                              
      REAL X(1)                                                                 
C                                                                               
      A      = X(1) - P(2)                                                      
      B      = DABS(A)                                                          
      C      = 1.098612289/P(3)                                                 
      D      = B*C                                                              
      E      = DEXP(D)                                                          
      F      = 1./ (1.+E)                                                       
      DY(1)  = 2.*F                                                             
      Y1     = DY(1)*P(1)                                                       
      F      = C*E*F                                                            
      DY(2)  = DSIGN(-Y1*F,A)                                                   
      DY(3)  = F*B/P(3)                                                         
      RETURN                                                                    
                                                                                
      END                                                                       
