da_find_fft_trig_funcs.inc

1 subroutine da_find_fft_trig_funcs(n, trig_functs)
2 
3    !---------------------------------------------------------------------------
4    ! Purpose: Set up constants required for Fourier, sine and cosine transforms
5    !---------------------------------------------------------------------------
6 
7    implicit none
8 
9    integer, intent(in)        :: n
10    real, intent(out)          :: trig_functs(:)
11 
12    integer                    :: k, nil, nhl
13    real                       :: del, angle
14 
15    !---------------------------------------------------------------------------
16    ! [1.0] Trig functions for real periodic transform:
17    !---------------------------------------------------------------------------
18 
19    trig_functs(:) = 0.0
20 
21    DEL=4.0*ASin(1.0)/FLOAT(N)
22    NIL=0
23    NHL=(N/2)-1
24 
25    do K=NIL,NHL
26       ANGLE=FLOAT(K)*DEL
27       trig_functs(2*K+1)=COS(ANGLE)
28       trig_functs(2*K+2)=Sin(ANGLE)
29    end do
30 
31    ! [1.1] Extra trig functions for cosine transform:
32 
33    DEL=0.5*DEL
34    do K=1,NHL
35       ANGLE=FLOAT(K)*DEL
36       trig_functs(2*N+K)=Sin(ANGLE)
37    end do
38   
39    ! [1.2] Extra trig functions for shifted cosine transform:
40 
41    DEL=0.5*DEL
42    do K=1,N
43       ANGLE=FLOAT(K)*DEL
44       trig_functs(N+K)=Sin(ANGLE)
45    end do
46 
47 end subroutine da_find_fft_trig_funcs
48 
49