      SUBROUTINE FFA99 (G,A,W,LOT)
      DIMENSION G( 50 ), A( 50 ), W( 50 )
C
      COMMON /FFTS/ IFAX(10), TRIGS( 50 ,2)
C
C  GENERAL MULTIPLE FAST FOURIER TRANSFORM - ANALYSIS.
C  GOOD FOR ZONAL WAVE NUMBER  16 .
C
C     DIMENSION G( 50 ,LOT), A( 50 ,LOT), W( 50 ,LOT)
C
C   INPUT - LOT SETS OF GRID VALUES IN
C           G(1,J), G(2,J), ..., G( 50 ,J), J=1,...,LOT.
C           G ARRAY IS NOT CHANGED BY SUBROUTINE FFA99.
C
C  OUTPUT - LOT SETS OF COMPLEX COEFFICIENTS IN
C           A(1,J), A(2,J), ..., A( 50 ,J), J=1,...,LOT.
C           COMPLEX COEFFICIENTS IN
C           A( 17 *2+1,J), ..., A( 50 ,J), J=1,...,LOT ARE NOT USED
C           OUTSIDE FFA99.
C
C  W IS A WORK ARRAY.
C
C  IFAX ARRAY IS SET FOR FFT99M
C              DURING FIRST USE OF FFS99 AND FFA99.
C  TRIGS ARRAY IS SET WITH SIN AND COS VALUES
C              DURING FIRST USE OF FFS99 AND FFA99.
      DATA ITEST/0/
      IF (ITEST.EQ.1)  GO TO 200
            ITEST=1
            CALL    FAX ( IFAX,  50 , 3)
            CALL FFTRIG (TRIGS,  50 , 3)
200   CONTINUE
C
C     COPY G ARRAY TO A ARRAY.
      IMAX= 50 *LOT
      DO 400 I=1,IMAX
            A(I)=G(I)
400   CONTINUE
C
C     CALL MODIFIED VERSION OF FFT99 FROM EUROPEAN CENTER.
      CALL FFT99M (A, W, TRIGS, IFAX, 1,  50 ,  50 , LOT, -1)
C
      RETURN
      END
