SUBROUTINE W3FT21(FLN,GN,PLN,EPS,FL,WORK,TRIGS,L1,L2,I2)
C$$$ SUBPROGRAM DOCUMENTATION BLOCK
C
C SUBPROGRAM: W3FT21 COMPUTES 2.5 X 2.5 N. HEMI. GRID-SCALER
C AUTHOR: JONES,R.E. ORG: W342 DATE: 81-11-19
C
C ABSTRACT: COMPUTES 2.5 X 2.5 N. HEMI. GRID OF 145 X 37 POINTS
C FROM SPECTRAL COEFFICIENTS IN A RHOMBOIDAL 30 RESOLUTION
C REPRESENTING A SCALAR FIELD. SPECIAL VERSION OF W3FT08 WHICH
C GIVES PROGRAMMER MORE CONTROL OF HOW MANY WAVES ARE SUMMED
C AND HOW MANY POINTS IN EACH WAVE. A PROGRAMMER CAN SIMULATE
C 24-MODE, 12-MODE, ETC.
C
C PROGRAM HISTORY LOG:
C 81-11-19 R.E.JONES
C 84-06-01 R.E.JONES CHANGE TO IBM VS FORTRAN
C
C USAGE: CALL W3FT21(FLN,GN,PLN,EPS,FL,WORK,TRIGS,L1,L2,I2)
C
C INPUT VARIABLES:
C NAMES INTERFACE DESCRIPTION OF VARIABLES AND TYPES
C ------ --------- -----------------------------------------------
C FLN ARG LIST 961 COMPLEX COEFF.
C PLN ARG LIST 992 REAL SPACE FOR LEGENDRE POLYNOMIALS
C EPS ARG LIST 992 REAL SPACE FOR
C COEFFS. USED IN COMPUTING PLN.
C FL ARG LIST 31 COMPLEX SPACE FOR FOURIER COEFF.
C WORK ARG LIST 144 REAL WORK SPACE FOR SUBR. W3FT12
C TRIGS ARG LIST 216 PRECOMPUTED TRIG FUNCS, USED
C IN W3FT12, COMPUTED BY W3FA13
C L1 ARG LIST STARTING WAVE NUMBER
C L2 ARG LIST ENDING WAVE NUMBER
C I2 ARG LIST MODE OF SPECTRAL COEFFICIENTS
C
C OUTPUT VARIABLES:
C NAMES INTERFACE DESCRIPTION OF VARIABLES AND TYPES
C ------ --------- -----------------------------------------------
C GN ARG LIST (145,37) GRID VALUES.
C 5365 POINT GRID IS TYPE 29 OR 1D HEX O.N. 84
C
C SUBPROGRAMS CALLED:
C NAMES LIBRARY
C ------------------------------------------------------- --------
C AIMAG CMPLX REAL SYSLIB
C W3FA12 W3FT12 W3LIB
C
C WARNING: THIS SUBROUTINE WAS OPTIMIZED TO RUN IN A SMALL AMOUNT OF
C MEMORY, IT IS NOT OPTIMIZED FOR SPEED, 70 PERCENT OF THE TIME IS
C USED BY SUBROUTINE W3FA12 COMPUTING THE LEGENDRE POLYNOMIALS. SINCE
C THE LEGENDRE POLYNOMIALS ARE CONSTANT THEY NEED TO BE COMPUTED
C ONLY ONCE IN A PROGRAM. BY MOVING W3FA12 TO THE MAIN PROGRAM AND
C COMPUTING PLN AS A (32,31,37) ARRAY AND CHANGING THIS SUBROUTINE
C TO USE PLN AS A THREE DIMENSION ARRAY YOU CAN CUT THE RUNNING TIME
C 70 PERCENT.
C
C ATTRIBUTES:
C LANGUAGE: CRAY CFT77 FORTRAN
C MACHINE: CRAY C916, Y-MP8/64, Y-MP EL92/256
C
C$$$
C
COMPLEX FL (31)
COMPLEX FLN (31,31)
C
REAL COLRA
REAL EPS (992)
C
REAL GN (145,37)
REAL PLN (32,31)
REAL TRIGS (216)
REAL WORK (144)
C
SAVE
C
DATA PI /3.14159265/
C
DRAD = 2.5 * PI / 180.0
C
K1 = L1 + 1
K2 = L2 + 1
M2 = I2 + 1
C
DO 400 LAT = 1,37
LATN = 38 - LAT
COLRA = (LAT-1) * DRAD
CALL W3FA12 (PLN, COLRA, 30 ,EPS)
C
DO 100 L = 1, 31
FL(L) = (0.,0.)
100 CONTINUE
C
DO 300 L = K1 , K2
DO 200 I = 1 , M2
FL(L) = FL(L) + CMPLX(PLN(I,L) * REAL(FLN(I,L)) ,
& PLN(I,L) * AIMAG(FLN(I,L)) )
200 CONTINUE
C
300 CONTINUE
C
CALL W3FT12(FL,WORK,GN(1,LATN),TRIGS)
C
400 CONTINUE
C
RETURN
END