added array functions and scale function

include/utility.hpp

@@ -4,6 +4,8 @@
 #include <exception>
 #include <limits>
 #include <iostream>
+#include <glm/glm.hpp>
+#include <glm/gtc/type_ptr.hpp>
 
 #define BAD_Z_VALUE -999999.
 
@@ -22,8 +24,13 @@ std::array<double, 3> extract_triplet(const std::string& str_in, size_t& start);
 /*i: column, j: row. unsigned for opengl compatibility*/
 unsigned ij2index(unsigned i, unsigned j, unsigned Ny);
 
+std::array<float, 3> operator+=(std::array<float, 3>&, const std::array<float, 3>&);
 
+std::array<float, 3> cross(const std::array<float, 3>&, const std::array<float, 3>&);
 
+std::array<float, 3> operator/=(std::array<float, 3>&, const float);
+
+glm::mat4 scale_z(float z0, float factor);
 
 
 
@@ -56,4 +63,4 @@ double max(const T& container, size_t offset, size_t stride) {
 		}
 	}
 	return max_val;
-}
\ No newline at end of file
+}