[FEAT] Matrix Add invertible method

raytracing/src/matrix.cpp

@@ -203,7 +203,17 @@ bool Matrix::transpose(void)
 
 double Matrix::determinant(void)
 {
+    double the_det = 0;
+
+    if (m_rows == 2)
         return (m_data[0][0] * m_data[1][1]) - (m_data[0][1] * m_data[1][0]);
+
+    for (int the_col = 0; the_col < m_cols; the_col++)
+    {
+        the_det += m_data[0][the_col] * cofactor(0, the_col);
+    }
+
+    return the_det;
 }
 
 /* ------------------------------------------------------------------------- */
@@ -247,6 +257,16 @@ double Matrix::cofactor(uint8_t a_row, uint8_t a_col)
 
 /* ------------------------------------------------------------------------- */
 
+bool Matrix::invertible(void)
+{
+    if (determinant() == 0)
+        return false;
+
+    return true;
+}
+
+/* ------------------------------------------------------------------------- */
+
 Matrix Matrix::identity(void)
 {
     Matrix the_identity = {

raytracing/src/matrix.h

@@ -65,6 +65,8 @@ namespace Raytracer
         double minor(uint8_t a_row, uint8_t a_col);
         double cofactor(uint8_t a_row, uint8_t a_col);
 
+        bool invertible(void);
+
         static Matrix identity(void);
 
     private:

tests/03_matrix.cpp

@@ -334,6 +334,7 @@ TEST_CASE("[Matrix] Calculating the determinant of a 4x4 matrix", "[Matrix]")
     Matrix a = {
         {-2, -8,  3,  5},
         {-3,  1,  7,  3},
+        { 1,  2, -9,  6},
         {-6,  7,  7, -9}
     };
 
@@ -343,3 +344,33 @@ TEST_CASE("[Matrix] Calculating the determinant of a 4x4 matrix", "[Matrix]")
     REQUIRE(a.cofactor(0, 3) == 51);
     REQUIRE(a.determinant() == -4071);
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] Testing an invertible matrix for invertibility", "[Matrix]")
+{
+    Matrix a = {
+        {6,  4, 4,  4},
+        {5,  5, 7,  6},
+        {4, -9, 3, -7},
+        {9,  1, 7, -6}
+    };
+
+    REQUIRE(a.determinant() == -2120);
+    REQUIRE(a.invertible() == true);
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] Testing an noninvertible matrix for invertibility", "[Matrix]")
+{
+    Matrix a = {
+        {-4,  2, -2, -3},
+        { 9,  6,  2,  6},
+        { 0, -5,  1, -5},
+        { 0,  0,  0,  0}
+    };
+
+    REQUIRE(a.determinant() == 0);
+    REQUIRE(a.invertible() == false);
+}