...

cxx/fitpack/fitpack.h

@@ -333,4 +333,37 @@ int fitpack_eval_spl2d(const TXT& tx,
     return ier;
 }
 
+
+// scalar x,y version
+template <std::ranges::contiguous_range TXT,
+          std::ranges::contiguous_range TYT,
+          typename XT,
+          typename YT,
+          std::ranges::contiguous_range CoeffT,
+          typename FuncT>
+int fitpack_eval_spl2d(const TXT& tx,
+                       const TYT& ty,
+                       const CoeffT& coeffs,
+                       const XT& x,
+                       const YT& y,
+                       FuncT& func,
+                       int kx = 3,
+                       int ky = 3)
+{
+    static_assert(std::same_as<std::ranges::range_value_t<TXT>, double> &&
+                      std::same_as<std::ranges::range_value_t<TYT>, double> &&
+                      std::same_as<std::ranges::range_value_t<CoeffT>, double>,
+                  "Input ranges elements type must be double!");
+
+    static_assert(
+        std::convertible_to<XT, double> && std::convertible_to<YT, double> && std::convertible_to<FuncT, double>,
+        "XT, YT and FuncT types must be a scalar convertible to double!");
+
+    auto xv = std::vector<double>(1, x);
+    auto yv = std::vector<double>(1, y);
+    auto fv = std::vector<double>(1, func);
+
+    return fitpack_eval_spl2d(tx, ty, coeffs, xv, yv, fv, kx, ky);
+}
+
 }  // namespace mcc::fitpack