solved issue with magic number not compiling

Author: salva24

src/forces_tumor_cart.cc

@@ -61,7 +61,6 @@ Real4 InteractionVelocity::Calculate(const Agent* lhs, const Agent* rhs) const {
                          displacement[2] * displacement[2];
   const real_t distance = std::max(std::sqrt(dist_sq), kEpsilonDistance);
 
-  constexpr real_t kHalf = 2.0;
   const real_t radius_a = a->GetDiameter() / kHalf;
   const real_t radius_b = b->GetDiameter() / kHalf;
   const real_t combined_radius = radius_a + radius_b;

src/hyperparams.h

@@ -139,6 +139,9 @@ constexpr real_t kTimeApoptosis = 8.6 * 60;
 /// Reduction of consumption rate of dead cells when they enter necrosis
 constexpr real_t kReductionConsumptionDeadCells = 0.1;
 
+/// Constant for division by 2.0
+constexpr real_t kHalf = 2.0;
+
 /// Chemicals
 ///  Number of voxels per axis for the substances grid
 constexpr int kResolutionGridSubstances = 50;