SUBROUTINE COST(N,X,WSAVE)
C***BEGIN PROLOGUE  COST
C***DATE WRITTEN   790601   (YYMMDD)
C***REVISION DATE  830401   (YYMMDD)
C***CATEGORY NO.  J1A3
C***KEYWORDS  FOURIER TRANSFORM
C***AUTHOR  SWARZTRAUBER, P. N., (NCAR)
C***PURPOSE  Cosine transform of a real, even sequence.
C***DESCRIPTION
C
C  Subroutine COST computes the discrete Fourier cosine transform
C  of an even sequence X(I).  The transform is defined below at output
C  parameter X.
C
C  COST is the unnormalized inverse of itself since a call of COST
C  followed by another call of COST will multiply the input sequence
C  X by 2*(N-1).  The transform is defined below at output parameter X.
C
C  The array WSAVE which is used by subroutine COST must be
C  initialized by calling subroutine COSTI(N,WSAVE).
C
C  Input Parameters
C
C  N       the length of the sequence X.  N must be greater than 1.
C          The method is most efficient when N-1 is a product of
C          small primes.
C
C  X       an array which contains the sequence to be transformed
C
C  WSAVE   a work array which must be dimensioned at least 3*N+15
C          in the program that calls COST.  The WSAVE array must be
C          initialized by calling subroutine COSTI(N,WSAVE), and a
C          different WSAVE array must be used for each different
C          value of N.  This initialization does not have to be
C          repeated so long as N remains unchanged.  Thus subsequent
C          transforms can be obtained faster than the first.
C
C  Output Parameters
C
C  X       For I=1,...,N
C
C             X(I) = X(1)+(-1)**(I-1)*X(N)
C
C               + the sum from K=2 to K=N-1
C
C                   X(K)*COS((K-1)*(I-1)*PI/(N-1))
C
C               A call of COST followed by another call of
C               COST will multiply the sequence X by 2*(N-1).
C               Hence COST is the unnormalized inverse
C               of itself.
C
C  WSAVE   contains initialization calculations which must not be
C          destroyed between calls of COST.
C***REFERENCES  (NONE)
C***ROUTINES CALLED  RFFTF
C***END PROLOGUE  COST