Implement functions to create our desired matrix

include/matrix.hpp

@@ -0,0 +1,16 @@
+#ifndef __MATRIX__
+#define __MATRIX__
+
+#include <armadillo>
+
+
+arma::mat create_tridiagonal(
+    const arma::vec& a, 
+    const arma::vec& d, 
+    const arma::vec& e);
+
+arma::mat create_tridiagonal(int n, double a, double d, double e);
+
+arma::mat create_symmetric_tridiagonal(int n, double a, double d);
+
+#endif