add get_taper() function

nifty_gridder.cc

@@ -310,6 +310,31 @@ vector<double> correction_factors (size_t n, size_t nval, size_t w)
   return res;
   }
 
+constexpr auto get_taper_DS = R"""(
+Returns the correction coefficients.
+
+Parameters
+==========
+ndirty : integer
+    the number of pixels on the dirty image in the desired direction
+epsilon : np.float64
+    the gridder epsilon
+
+Returns
+=======
+np.array((ndirty,), dtype=np.float64)
+    the correction factors.
+)""";
+pyarr_c<double> get_taper(size_t ndirty, double epsilon)
+  {
+  auto tmp = correction_factors(2*ndirty, ndirty, get_w(epsilon));
+  auto res = makeArray<double>({ndirty});
+  auto vres = res.mutable_data();
+  for (size_t i=0; i<ndirty; ++i)
+    vres[i] = tmp[i];
+  return res;
+  }
+
 template<typename T> struct UVW
   {
   T u, v, w;
@@ -1412,4 +1437,5 @@ PYBIND11_MODULE(nifty_gridder, m)
     "idx"_a, "grid"_a, "wgt"_a, "ms_in"_a=None);
   m.def("apply_holo",&apply_holo<double>, "baselines"_a, "gconf"_a, "idx"_a,
     "grid"_a);
+  m.def("get_taper",&get_taper, get_taper_DS, "n"_a, "epsilon"_a);
   }