feat(meshIO): LinearRescale method added

Rescaling a mesh by a linear transformation is a useful option so that we can start with a single "base" mesh and then rescale it to the dimensions needed for our problem. This commit adds the LinearRescale option too meshIO so that a unit sphere can be turned into a sphere of arbitrary radius (as an example).

src/meshIO/private/meshIO.cpp

@@ -2,11 +2,12 @@
 #include <string>
 #include <iostream>
 #include <fstream>
+#include <stdexcept>
 
 #include "meshIO.h"
 
 
-MeshIO::MeshIO(const std::string &mesh_file)
+MeshIO::MeshIO(const std::string &mesh_file, double scale_factor)
 {
     mesh_file_ = mesh_file;
     std::ifstream mesh_stream(mesh_file);
@@ -19,6 +20,7 @@ MeshIO::MeshIO(const std::string &mesh_file)
     {
         mesh_ = mfem::Mesh(mesh_stream, 1, 10);
         loaded_ = true;
+        if (scale_factor != 1.0) { LinearRescale(scale_factor); }
     }
 }
 
@@ -26,6 +28,32 @@ MeshIO::~MeshIO()
 {
 }
 
+void MeshIO::LinearRescale(double scale_factor) {
+    if (!loaded_) {
+        throw std::runtime_error("Mesh not loaded before rescaling.");
+    }
+
+    if (scale_factor <= 0.0) {
+        throw std::invalid_argument("Scale factor must be positive.");
+    }
+
+    // Ensure there are nodes even for linear order meshes
+    mesh_.EnsureNodes();
+    const mfem::GridFunction *nodes = mesh_.GetNodes();
+    double *node_data = nodes->GetData();  // THIS IS KEY
+
+    int data_size = nodes->Size();
+
+    for (int i = 0; i < data_size; ++i) {
+        node_data[i] *= scale_factor;
+    }
+
+    // nodes->Update(); /updates the fespace
+    mesh_.NodesUpdated();
+ 
+
+}
+
 bool MeshIO::IsLoaded() const
 {
     return loaded_;