Sync public subset from Flux (private)

include/numerics/interpolation1d/interpolation1d_linear.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "./numerics/interpolation1d/interpolation1d_base.h"
+
+
+namespace numerics{
+	
+	template <typename T>
+	struct interp_linear : Base_interp<T> {
+		using Base   = Base_interp<T>;
+	  	// bring base data members into scope (or use this->xx / this->yy below)
+	  	using Base::xx;
+	  	using Base::yy;
+
+
+		interp_linear(const utils::Vector<T> &xv, const utils::Vector<T> &yv): Base_interp<T>(xv, &yv[0], 2){}
+
+		T rawinterp(int64_t j, T x) override{
+			if (xx[j]==xx[j+1]){
+				return yy[j]; 			// Table is defective, but we can recover.
+			}else {
+				return (yy[j] + ((x-xx[j])/(xx[j+1]-xx[j]))*(yy[j+1]-yy[j]));
+			}
+		}
+
+	};
+
+} // namespace numerics
+