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#ifndef NAVIERSTOKES_H
#define NAVIERSTOKES_H
#include <complex.h>
#include <fftw3.h>
// to extract elements from array of size S representing a function of momentum, use
// array[KEXTRACT(kx,ky,size)]
#define KLOOKUP(X,Y,S) (X>=0?X:S+X)*S+(Y>=0?Y:S+Y)
// parameters for the NS equation
typedef struct ns_params {
// number of modes
int K;
// 2*K+1
int S;
// 4*K+1
int N;
// forcing term
_Complex double* g;
// time step
double h;
// friction
double nu;
} ns_params;
// arrays on which the ffts are performed
typedef struct fft_vects {
fftw_complex* fft1;
fftw_complex* fft2;
fftw_complex* invfft;
fftw_plan fft1_plan;
fftw_plan fft2_plan;
fftw_plan invfft_plan;
} fft_vects;
// next time step for Irreversible Navier-Stokes equation
int ins_step(_Complex double* u, ns_params params, fft_vects vects, _Complex double* tmp1, _Complex double* tmp2, _Complex double* tmp3);
// right side of Irreversible Navier-Stokes equation
int ins_rhs(_Complex double* out, _Complex double* u, ns_params params, fft_vects vects);
// compute alpha
_Complex double compute_alpha(_Complex double* u, ns_params params);
#endif
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