c four1 -- this is the four1 routine from numerical recipes SUBROUTINE FOUR1(DATA,NN,ISIGN) REAL*8 WR,WI,WPR,WPI,WTEMP,THETA DIMENSION DATA(*) N=2*NN J=1 DO 11 I=1,N,2 IF(J.GT.I)THEN TEMPR=DATA(J) TEMPI=DATA(J+1) DATA(J)=DATA(I) DATA(J+1)=DATA(I+1) DATA(I)=TEMPR DATA(I+1)=TEMPI ENDIF M=N/2 1 IF ((M.GE.2).AND.(J.GT.M)) THEN J=J-M M=M/2 GO TO 1 ENDIF J=J+M 11 CONTINUE MMAX=2 2 IF (N.GT.MMAX) THEN ISTEP=2*MMAX THETA=6.28318530717959D0/(ISIGN*MMAX) WPR=-2.D0*DSIN(0.5D0*THETA)**2 WPI=DSIN(THETA) WR=1.D0 WI=0.D0 DO 13 M=1,MMAX,2 DO 12 I=M,N,ISTEP J=I+MMAX TEMPR=SNGL(WR)*DATA(J)-SNGL(WI)*DATA(J+1) TEMPI=SNGL(WR)*DATA(J+1)+SNGL(WI)*DATA(J) DATA(J)=DATA(I)-TEMPR DATA(J+1)=DATA(I+1)-TEMPI DATA(I)=DATA(I)+TEMPR DATA(I+1)=DATA(I+1)+TEMPI 12 CONTINUE WTEMP=WR WR=WR*WPR-WI*WPI+WR WI=WI*WPR+WTEMP*WPI+WI 13 CONTINUE MMAX=ISTEP GO TO 2 ENDIF RETURN END