better, but not OK yet

nifty_gridder.cc

@@ -594,6 +594,9 @@ template<typename T> class GridderConfig
     complex<T> wscreen(double x, double y, double w, bool adjoint) const
       {
       constexpr double pi = 3.141592653589793238462643383279502884197;
+// PhD : sqrt (1-x*x-y*y)) - 1
+//here 1 - sin(sqrt(x*x+y*y))**2/(1.+cos(sqrt(x*x+y*y)))
+// ==   (cos(sqrt(x*x+y*y))**2 +cos(sqrt(x*x+y*y)))  / (1.+cos(sqrt(x*x+y*y)))
       double eps = sqrt(x+y);
       double s = sin(eps);
       double nm1 = -s*s/(1.+cos(eps));
@@ -1539,12 +1542,14 @@ myassert(cnt<nvis_plane[iw],"must not happen");
         idx_loc[cnt] = idx[ipart];
         ++cnt;
         }
+myassert(cnt==nvis_plane[iw],"must not happen 2");
     auto dirty_ = gconf.apply_wscreen(
       gconf.grid2dirty_c(vis2grid_c(baselines, gconf, idx_loc_, vis_loc_, None, None)), wcur, false);
     auto dirty = dirty_.data();
     for (ptrdiff_t i=0; i<accum_.size(); ++i)
       accum[i] += dirty[i];
     }
+
   // correct for w gridding
   {
   py::gil_scoped_release release;
@@ -1565,16 +1570,21 @@ cout << "applying correction for gridding in w direction" << endl;
 #pragma omp for schedule(static)
   for (size_t i=0; i<=nx_dirty/2; ++i)
     {
-    double fx = x0+i*psx;
+//    double fx = x0+i*psx;
+    double fx = -0.5+i*1./nx_dirty;
     fx *= fx;
     for (size_t j=0; j<=ny_dirty/2; ++j)
       {
-      double fy = y0+j*psy;
+//      double fy = y0+j*psy;
+      double fy = -0.5+j*1./ny_dirty;
       fy*=fy;
-      auto n=sqrt(1.-fx-fy)-1.;
+  //    auto n=sqrt(1.-fx-fy)-1.;
+      auto n=cos(sqrt(fx+fy)) -1;
+//      cout << n << endl;
       double fct = 0.;
       for (int i=0; i<p; ++i)
         fct += wgt[i]*psi[i]*cos(pi*w_supp*n*x[i]);
+//      cout << fct << endl;
       fct = 1./(w_supp*fct);
       if ((i==nx_dirty/2) &&(j==ny_dirty/2))
         cout << i << " " << j << " " << fct << endl;