add convenience function to compute accuracy from support and oversampling factor

pyinterpol_ng/interpol_ng.h

@@ -535,9 +535,13 @@ template<typename T> class Interpolator
       }
   };
 
+double epsilon_guess(size_t support, double ofactor)
+  { return std::sqrt(12.)*std::exp(-(support*ofactor)); }
+
 }
 
 using detail_interpol_ng::Interpolator;
+using detail_interpol_ng::epsilon_guess;
 
 }
 

pyinterpol_ng/pyinterpol_ng.cc

@@ -256,4 +256,5 @@ PYBIND11_MODULE(pyinterpol_ng, m)
   m.def("rotate_alm", &pyrotate_alm<fptype>, "alm"_a, "lmax"_a, "psi"_a, "theta"_a,
     "phi"_a);
 #endif
+  m.def("epsilon_guess", &epsilon_guess, "support"_a, "ofactor"_a);
   }