From d8380602656b54649c46bac93876b814b4d8eba7 Mon Sep 17 00:00:00 2001
From: Ian Jauslin <ian.jauslin@rutgers.edu>
Date: Tue, 25 Apr 2023 17:51:14 -0400
Subject: Remove terms with kx=0 and ky<=0

---
 src/navier-stokes.c | 52 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

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

diff --git a/src/navier-stokes.c b/src/navier-stokes.c
index 153631b..51d198c 100644
--- a/src/navier-stokes.c
+++ b/src/navier-stokes.c
@@ -241,12 +241,12 @@ int  ns_init_tmps(
   unsigned int nthreads
 ){
   // velocity field
-  *u=calloc(sizeof(_Complex double),(K1+1)*(2*K2+1));
+  *u=calloc(sizeof(_Complex double),K1*(2*K2+1)+K2);
 
   // allocate tmp vectors for computation
-  *tmp1=calloc(sizeof(_Complex double),(K1+1)*(2*K2+1));
-  *tmp2=calloc(sizeof(_Complex double),(K1+1)*(2*K2+1));
-  *tmp3=calloc(sizeof(_Complex double),(K1+1)*(2*K2+1));
+  *tmp1=calloc(sizeof(_Complex double),K1*(2*K2+1)+K2);
+  *tmp2=calloc(sizeof(_Complex double),K1*(2*K2+1)+K2);
+  *tmp3=calloc(sizeof(_Complex double),K1*(2*K2+1)+K2);
 
   // init threads
   fftw_init_threads();
@@ -303,7 +303,7 @@ int copy_u(
 ){
   int i;
 
-  for(i=0;i<(K1+1)*(2*K2+1);i++){
+  for(i=0;i<K1*(2*K2+1)+K2;i++){
     u[i]=u0[i];
   }
 
@@ -335,14 +335,14 @@ int ns_step(
   ns_rhs(tmp1, u, K1, K2, N1, N2, nu, L, g, fft1, fft2, ifft, irreversible);
   // add to output
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp3[klookup_sym(kx,ky,K2)]=u[klookup_sym(kx,ky,K2)]+delta/6*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
 
   // u+h*k1/2
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp2[klookup_sym(kx,ky,K2)]=u[klookup_sym(kx,ky,K2)]+delta/2*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
@@ -350,14 +350,14 @@ int ns_step(
   ns_rhs(tmp1, tmp2, K1, K2, N1, N2, nu, L, g, fft1, fft2, ifft, irreversible);
   // add to output
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp3[klookup_sym(kx,ky,K2)]+=delta/3*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
 
   // u+h*k2/2
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp2[klookup_sym(kx,ky,K2)]=u[klookup_sym(kx,ky,K2)]+delta/2*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
@@ -365,14 +365,14 @@ int ns_step(
   ns_rhs(tmp1, tmp2, K1, K2, N1, N2, nu, L, g, fft1, fft2, ifft, irreversible);
   // add to output
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp3[klookup_sym(kx,ky,K2)]+=delta/3*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
 
   // u+h*k3
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       tmp2[klookup_sym(kx,ky,K2)]=u[klookup_sym(kx,ky,K2)]+delta*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
@@ -380,7 +380,7 @@ int ns_step(
   ns_rhs(tmp1, tmp2, K1, K2, N1, N2, nu, L, g, fft1, fft2, ifft, irreversible);
   // add to output
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
       u[klookup_sym(kx,ky,K2)]=tmp3[klookup_sym(kx,ky,K2)]+delta/6*tmp1[klookup_sym(kx,ky,K2)];
     }
   }
@@ -417,14 +417,12 @@ int ns_rhs(
     alpha=compute_alpha(u,K1,K2,g,L);
   }
 
-  for(i=0; i<(K1+1)*(2*K2+1); i++){
+  for(i=0; i<K1*(2*K2+1)+K2; i++){
     out[i]=0;
   }
   for(kx=0;kx<=K1;kx++){
-    for(ky=-K2;ky<=K2;ky++){
-      if(kx!=0 || ky!=0){
-        out[klookup_sym(kx,ky,K2)]=-4*M_PI*M_PI/L/L*alpha*(kx*kx+ky*ky)*u[klookup_sym(kx,ky,K2)]+g[klookup_sym(kx,ky,K2)]+4*M_PI*M_PI/L/L/sqrt(kx*kx+ky*ky)*ifft.fft[klookup(kx,ky,N1,N2)];
-      }
+    for(ky=(kx>0 ? -K2 : 1);ky<=K2;ky++){
+      out[klookup_sym(kx,ky,K2)]=-4*M_PI*M_PI/L/L*alpha*(kx*kx+ky*ky)*u[klookup_sym(kx,ky,K2)]+g[klookup_sym(kx,ky,K2)]+4*M_PI*M_PI/L/L/sqrt(kx*kx+ky*ky)*ifft.fft[klookup(kx,ky,N1,N2)];
     }
   }
 
@@ -610,7 +608,7 @@ int klookup(
   return (kx>=0 ? kx : S1+kx)*S2 + (ky>=0 ? ky : S2+ky);
 }
 
-// get index for kx,ky in array of size K1,K2 in which only the terms with kx>=0 are stored
+// get index for kx,ky in array of size K1,K2 in which only the terms with kx>=0 and if kx=0, ky>0 are stored
 int klookup_sym(
   int kx,
   int ky,
@@ -620,7 +618,14 @@ int klookup_sym(
     fprintf(stderr, "bug!: attempting to access a symmetrized vector at kx<0\n Contact Ian at ian.jauslin@rutgers.edu!\n");
     exit(-1);
   }
-  return kx*(2*K2+1) + (ky>=0 ? ky : (2*K2+1)+ky);
+  if (kx==0) {
+    if (ky<=0){
+      fprintf(stderr, "bug!: attempting to access a symmetrized vector at kx=0 and ky<=0\n Contact Ian at ian.jauslin@rutgers.edu!\n");
+      exit(-1);
+    }
+    return ky-1;
+  }
+  return K2+(kx-1)*(2*K2+1) + (ky>=0 ? ky : (2*K2+1)+ky);
 }
 
 // get u_{kx,ky} from a vector u in which only the values for kx>=0 are stored, assuming u_{-k}=u_k^*
@@ -630,5 +635,12 @@ _Complex double getval_sym(
   int ky,
   int K2
 ){
-  return (kx>=0 ? u[klookup_sym(kx,ky,K2)] : conj(u[klookup_sym(-kx,-ky,K2)]));
+  if(kx>0 || (kx==0 && ky>0)){
+    return u[klookup_sym(kx,ky,K2)];
+  }
+  else if(kx==0 && ky==0){
+    return 0;
+  } else {
+    return conj(u[klookup_sym(-kx,-ky,K2)]);
+  }
 }
-- 
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