TheAlgorithms · THIRU-1074 · Jun 23, 2023 · Jun 23, 2023 · Jun 23, 2023 · Jun 25, 2023
@@ -1,55 +1,51 @@
-package com.thealgorithms.maths;
-
-import java.util.*;
-
-/*
- * @author Ojasva Jain
- * Determinant of Matrix Wikipedia link : https://en.wikipedia.org/wiki/Determinant
- */
-public class DeterminantOfMatrix {
-
-    // Determinant calculator
-    //@return determinant of the input matrix
-    static int determinant(int[][] a, int n) {
-        int det = 0, sign = 1, p = 0, q = 0;
-        if (n == 1) {
-            det = a[0][0];
-        } else {
-            int[][] b = new int[n - 1][n - 1];
-            for (int x = 0; x < n; x++) {
-                p = 0;
-                q = 0;
-                for (int i = 1; i < n; i++) {
-                    for (int j = 0; j < n; j++) {
-                        if (j != x) {
-                            b[p][q++] = a[i][j];
-                            if (q % (n - 1) == 0) {
-                                p++;
-                                q = 0;
-                            }
-                        }
-                    }
-                }
-                det = det + a[0][x] * determinant(b, n - 1) * sign;
-                sign = -sign;
-            }
-        }
-        return det;
-    }
-
-    // Driver Method
-    public static void main(String[] args) {
-        Scanner in = new Scanner(System.in);
-        // Input Matrix
-        System.out.println("Enter matrix size (Square matrix only)");
-        int n = in.nextInt();
-        System.out.println("Enter matrix");
-        int[][] a = new int[n][n];
-        for (int i = 0; i < n; i++) {
-            for (int j = 0; j < n; j++) {
-                a[i][j] = in.nextInt();
-            }
-        }
-        System.out.println(determinant(a, n));
-    }
-}
+package com.thealgorithms.maths;
+import java.util.*;
+/*
+ * Determinant of Matrix :https://textbooks.math.gatech.edu/ila/determinants-cofactors.html
+ */
+public class DeterminantOfMatrix {
+    public static double[][] submatrix(double[][] mat,int order,int c) {
+        //creating reference for the sub matrix
+        double[][] subMat=new double[order-1][order-1];
+        //sub_c stores the column column index of the sub matrix
+        int subC;
+        for(int i=1;i<order;i++) {	
+            //making the column count zero after each row-addition
+            subC=0;
+            for(int k=0;k<order;k++) {
+                if(k==c) {
+                    continue;//skipping the column where the mat[0][c] of operation is in
+                }
+                subMat[i-1][subC]=mat[i][k];
+                subC+=1;//increasing the column count
+            }
+        }
+        return(subMat);
+    }
+    public static double determinant(double[][] mat,int order) {
+        /*determinant of the matrix with one element(order 1) :
+        is the element itself*/
+        if (order==1) {
+            return(mat[0][0]);
+        }
+        return(operation(mat,order));
+    }
+    public static double operation(double[][] mat,int order) {
+        int check;
+        double det=0;
+        for(int c=0;c<order;++c) {
+            if(c%2==0) {
+                check=1;
+            }
+            else {
+                check=-1;
+            }
+            det+=(check*(mat[0][c])*determinant(submatrix(mat,order,c),order-1));
+        }
+        return(det);
+    }
+}
+/*the above code will work for all square matrix whose order are greater than one.
+---to initiate this recursive algorithm pass the matrix and its order to the operation() method
+---if the order is 1 return the determinant of the matrix directly
+(determinant of the matrix with one element(order 1) :is the element itself)*/
@@ -0,0 +1,24 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class DeterminantOfMatrixTest {
+
+    @Test
+    void testDeterminantOfMatrix() {
+        double[][] matrix1 = { { 1, 0, 0}, {0, 1, 0}, {0, 0, 1} };
+        assertEquals(1.0, DeterminantOfMatrix.operation(matrix1, 3));
+
+        double[][] matrix2 = { { 2.0, 3.0 }, { -4.0, 5.0 } };
+        assertEquals(22.0, DeterminantOfMatrix.operation(matrix2, 2));
+
+        double[][] matrix3 = { { -1.0, 2.5, 3.0 }, { 4.0, -5.2, 6.0 }, { 7.3, -8.1, 9.6 } };
+        assertEquals(31.50000000000001, DeterminantOfMatrix.operation(matrix3, 3));
+
+        double[][] matrix4 = { {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 0, 1, 2}, {3, 4, 5, 6} };
+        assertEquals(0.0, DeterminantOfMatrix.operation(matrix4, 4));
+
+    }
+}