REAL*8 FUNCTION FARSD1(ALAM)
C***********************************************************************
C  In the calling routine a call to INIT must be made prior to calling *
C  this routine for the first time.                                    *
C***********************************************************************    
C  This function evaluates the product of the spectral density function
C  of a univariate autogregressive process, and the function
C  cos(lambda*tau), at the frequencies lambdaC  Inputs:
C  ALAM      Lambda
C  Inputs (/AUAR/):
C  B         Coefficients of autoregression
C  H         Precision of shock to autoregression
C  TAU       tau
C  NP        Number of coefficients in autoregression
C  Output:
C  FARSD1    Value of product described above
      IMPLICIT REAL*8 (A-H,O-Z)
      PARAMETER(LP=100)
      COMMON/AUAR/B(0:LP),H,TAU,NP
      COMMON/CONST/DLOG2,DLGPI,HLG2PI,PI,PII
      AL=ALAM
      AC=B(0)
      AS=0.0D0
      DO 10 IP=1,NP
      AC=AC+B(IP)*DCOS(AL*IP)
   10 AS=AS+B(IP)*DSIN(AL*IP)
      FARSD1=DCOS(AL*TAU)/(H*(AS**2+AC**2))
      RETURN
      END