!CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
!                                                                       
!   FFTPACK 5.0                                                         
!   Copyright (C) 1995-2004, Scientific Computing Division,             
!   University Corporation for Atmospheric Research                     
!   Licensed under the GNU General Public License (GPL)                 
!                                                                       
!   Authors:  Paul N. Swarztrauber and Richard A. Valent                
!                                                                       
!   $Id: mrfti1.f,v 1.2 2004/06/15 21:29:20 rodney Exp $                
!                                                                       
!CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
                                                                        
      SUBROUTINE MRFTI1 (N,WA,FAC) 
      REAL       WA(N)      ,FAC(15) 
      INTEGER    NTRYH(4) 
      DOUBLE PRECISION TPI,ARGH,ARGLD,ARG 
      DATA NTRYH(1),NTRYH(2),NTRYH(3),NTRYH(4)/4,2,3,5/ 
!                                                                       
      NL = N 
      NF = 0 
      J = 0 
  101 J = J+1 
      IF (J-4) 102,102,103 
  102 NTRY = NTRYH(J) 
      GO TO 104 
  103 NTRY = NTRY+2 
  104 NQ = NL/NTRY 
      NR = NL-NTRY*NQ 
      IF (NR) 101,105,101 
  105 NF = NF+1 
      FAC(NF+2) = NTRY 
      NL = NQ 
      IF (NTRY .NE. 2) GO TO 107 
      IF (NF .EQ. 1) GO TO 107 
      DO 106 I=2,NF 
         IB = NF-I+2 
         FAC(IB+2) = FAC(IB+1) 
  106 END DO 
      FAC(3) = 2 
  107 IF (NL .NE. 1) GO TO 104 
      FAC(1) = N 
      FAC(2) = NF 
      TPI = 8.D0*DATAN(1.D0) 
      ARGH = TPI/FLOAT(N) 
      IS = 0 
      NFM1 = NF-1 
      L1 = 1 
      IF (NFM1 .EQ. 0) RETURN 
      DO 110 K1=1,NFM1 
         IP = FAC(K1+2) 
         LD = 0 
         L2 = L1*IP 
         IDO = N/L2 
         IPM = IP-1 
         DO 109 J=1,IPM 
            LD = LD+L1 
            I = IS 
            ARGLD = FLOAT(LD)*ARGH 
            FI = 0. 
            DO 108 II=3,IDO,2 
               I = I+2 
               FI = FI+1. 
               ARG = FI*ARGLD 
               WA(I-1) = DCOS(ARG) 
               WA(I) = DSIN(ARG) 
  108       CONTINUE 
            IS = IS+IDO 
  109    CONTINUE 
         L1 = L2 
  110 END DO 
      RETURN 
      END