Function that takes a 2d STL vector and converts it to a (SUNDIALS defined) sparse matrix utilizing sundials internal functions.

vector_2d_to_sunmatrix.cpp

#include <iostream>
#include <vector>
#include <sunmatrix/sunmatrix_dense.h> // access to dense SUNMatrix
#include <sunmatrix/sunmatrix_sparse.h> // access to sparse SUNMatrix

// Converts 2d vector into a sparse matrix. This function assumes all the rows
// are the same size.
SUNMatrix convert_to_sparse(std::vector< std::vector< realtype > > vec) {
  // Defining the rows and columns.
  SUNMatrix temp_dense = SUNDenseMatrix(vec.size(), vec[0].size());
  realtype **temp_data =  SUNDenseMatrix_Cols(temp_dense);

  // Moving the vector values to the matrix, by element.
  for (int i = 0; i < vec.size(); i++) {
    for (int j = 0; j < vec[0].size(); j++) {
      temp_data[j][i] = vec[i][j];
    }
  }

  // Printing the 2d vector.
  std::cout << "2d Vector:\n\n";
  for (int i = 0; i < vec.size(); i++) {
    std::cout << "\n";
    for (int j = 0; j < vec[0].size(); j++) {
      std::cout << vec[i][j] << "\t";
    }
  }
  std::cout << "\n\n";

  std::cout << "Dense Matrix:\n";
  SUNDenseMatrix_Print(temp_dense, stdout);

  // SUNDIALS internal function conversion to sparse matrix. 
  SUNMatrix sparse = SUNSparseFromDenseMatrix(temp_dense, 0, CSR_MAT);
  
  std::cout << "Sparse Matrix:\n";
  SUNSparseMatrix_Print(sparse, stdout);
  
  // Free the memory used by the temporary dense matrix. 
  SUNMatDestroy(temp_dense);

  
  return sparse;
}