From c2c4804a89063b5ad5375806c2172d758100c116 Mon Sep 17 00:00:00 2001
From: Cory <cory@balaton.dev>
Date: Sun, 17 Sep 2023 14:42:25 +0200
Subject: [PATCH] Create test and correct some mistakes

---
 src/matrix.cpp     |  4 ++--
 src/test_suite.cpp | 28 +++++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/matrix.cpp b/src/matrix.cpp
index 1fa3536..f1099b7 100644
--- a/src/matrix.cpp
+++ b/src/matrix.cpp
@@ -17,8 +17,8 @@ arma::mat create_tridiagonal(
         A(i, i+1) = e(i);
     }
     
+    A(n-1, n-2) = a(n-2);
     A(n-1,n-1) = d(n-1);
-    A(n-1, n-2) = a(n-1);
 
     return A;
 }
@@ -26,7 +26,7 @@ arma::mat create_tridiagonal(
 arma::mat create_tridiagonal(int n, double a, double d, double e)
 {
     arma::vec a_vec = arma::vec(n-1, arma::fill::ones) * a;
-    arma::vec d_vec = arma::vec(n-1, arma::fill::ones) * d;
+    arma::vec d_vec = arma::vec(n, arma::fill::ones) * d;
     arma::vec e_vec = arma::vec(n-1, arma::fill::ones) * e;
 
     return create_tridiagonal(a_vec, d_vec, e_vec);
diff --git a/src/test_suite.cpp b/src/test_suite.cpp
index dc5d2ff..e92af50 100644
--- a/src/test_suite.cpp
+++ b/src/test_suite.cpp
@@ -1,9 +1,35 @@
+#include <cassert>
+#include <cmath>
 
+#include "matrix.hpp"
 
-void test_tridiag_setup() {
+void test_create_symmetric_tridiagonal() {
+    double tol = 10e-8;
+    double diff;
+    int N = 6;
+    double h = 1./(double) (N+1);
+    double a = -1. / (h*h), d = 2. / (h*h);
 
+    arma::mat A = create_symmetric_tridiagonal(N, a, d);
+
+    arma::vec eigval;
+    arma::mat eigvec;
+
+    arma::eig_sym(eigval, eigvec, A);
+
+    for (int i=0; i < N; i++) {
+        diff = eigval(i) - (d + 2.*a*std::cos(((i+1.)*M_PI)/(N+1.)));
+        assert(std::abs(diff) < tol); 
+    }
 }
 
 void test_max_off_diag_symmetric() {
 
 }
+
+int main() {
+
+    test_create_symmetric_tridiagonal();
+
+    return 0;
+}