From 6fbcb8665824b0c1edbbe8cb18d509ca7e006e49 Mon Sep 17 00:00:00 2001
From: Ian Jauslin <ian@jauslin.org>
Date: Thu, 19 May 2022 18:35:33 +0200
Subject: Compute energy

---
 src/navier-stokes.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

(limited to 'src/navier-stokes.c')

diff --git a/src/navier-stokes.c b/src/navier-stokes.c
index 18c2fc5..0a2842c 100644
--- a/src/navier-stokes.c
+++ b/src/navier-stokes.c
@@ -68,6 +68,55 @@ int uk(
   return(0);
 }
 
+// compute the energy as a function of time
+int energy(
+  int K1,
+  int K2,
+  int N1,
+  int N2,
+  unsigned int nsteps,
+  double nu,
+  double delta,
+  _Complex double (*g)(int,int),
+  unsigned int print_freq,
+  unsigned int nthreads
+){
+  _Complex double* u;
+  _Complex double* tmp1;
+  _Complex double* tmp2;
+  _Complex double* tmp3;
+  unsigned int t;
+  fft_vect fft1;
+  fft_vect fft2;
+  fft_vect ifft;
+  int kx,ky;
+  double energy;
+
+  ns_init_tmps(&u, &tmp1, &tmp2, &tmp3, &fft1, &fft2, &ifft, K1, K2, N1, N2, nthreads);
+  ns_init_u(u, K1, K2);
+
+  // iterate
+  for(t=0;t<nsteps;t++){
+    ins_step(u, K1, K2, N1, N2, nu, delta, g, fft1, fft2, ifft, tmp1, tmp2, tmp3);
+    
+    if(t%print_freq==0){
+
+      energy=0.;
+      for(kx=-K1;kx<=K1;kx++){
+	for (ky=-K2;ky<=K2;ky++){
+	  energy+=__real__ (u[klookup(kx,ky,2*K1+1,2*K2+1)]*conj(u[klookup(kx,ky,2*K1+1,2*K2+1)]));
+	}
+      }
+
+      fprintf(stderr,"%d % .8e % .8e\n",t,t*delta, energy);
+      printf("%8d % .15e % .15e\n",t,t*delta,energy);
+    }
+  }
+
+  ns_free_tmps(u, tmp1, tmp2, tmp3, fft1, fft2, ifft);
+  return(0);
+}
+
 // compute enstrophy as a function of time in the I-NS equation
 int enstrophy(
   int K1,
-- 
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