Add a lagrange file wrapper for the particles system

We should be able to use lagrange or spline as interpolator for the particles.

bfps/cpp/particles/particles_interp_lagrange.hpp

+#ifndef PARTICLES_INTER_SPLINE_HPP
+#define PARTICLES_INTER_SPLINE_HPP
+
+template <class real_number, int interp_neighbours>
+class particles_interp_lagrange;
+
+#include "Lagrange_polys.hpp"
+
+template <>
+class particles_interp_lagrange<double, 1>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n1(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 2>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n2(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 3>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n3(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 4>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n4(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 5>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n5(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 6>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n6(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 7>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n7(in_derivative, in_part_val, poly_val);
+    }
+};
+
+template <>
+class particles_interp_lagrange<double, 8>{
+public:
+    using real_number = double;
+
+    void compute_beta(const int in_derivative, const double in_part_val, double poly_val[]) const {
+        beta_Lagrange_n8(in_derivative, in_part_val, poly_val);
+    }
+};
+
+
+#endif