MuonR4 - Introduce mapping function between symmetric matrices & vectors

• Helper functions to establish a bijective mapping between the elements of a NxN matrix A with A_{ij} = A_{ji} and a linear vector
• Keep track which tube layer is the first from the second multilayer
• Hit sorting before creating the segment.

MuonSpectrometer/MuonPhaseII/MuonPatternRecognition/MuonPatternHelpers/MuonPatternHelpers/MatrixUtils.h

@@ -6,9 +6,11 @@
 #include <CxxUtils/ArrayHelper.h>
 #include <array>
 
-
 namespace MuonR4{
-
+    /** @brief Returns the sign of a number */
+    constexpr double sign(const double x) {
+        return  x > 0. ? 1. : x < 0. ? -1. : 0.;
+    }
     /** @brief Calculates the sum of 1 + 2 +3 +4 +... + k */
     constexpr unsigned int sumUp(unsigned k){
         return k*(k+1)/ 2;