Added closure-based initializer function for Matrix and corresponding unit test

Sources/Surge/Linear Algebra/Matrix.swift

@@ -65,6 +65,19 @@ public struct Matrix<Scalar> where Scalar: FloatingPoint, Scalar: ExpressibleByF
         self.grid = grid
     }
 
+    public init(rows: Int, columns: Int, _ closure: (_ row: Int, _ column: Int) throws -> Scalar) rethrows {
+        var grid: [Scalar] = []
+        grid.reserveCapacity(rows * columns)
+
+        for row in 0..<rows {
+            for column in 0..<columns {
+                grid.append(try closure(row, column))
+            }
+        }
+
+        self.init(rows: rows, columns: columns, grid: grid)
+    }
+
     public static func identity(size: Int) -> Matrix<Scalar> {
         return self.diagonal(rows: size, columns: size, repeatedValue: 1.0)
     }

Tests/SurgeTests/MatrixTests.swift

@@ -99,6 +99,22 @@ class MatrixTests: XCTestCase {
         XCTAssertEqual(actual, expected)
     }
 
+    func test_init_rows_columns_closure() {
+        typealias Scalar = Double
+
+        let columns = 4
+        let actual: Matrix<Scalar> = Matrix(rows: 3, columns: columns) { row, column in
+            Scalar((row * columns) + column)
+        }
+        let expected: Matrix<Scalar> = [
+            [0, 1, 2, 3],
+            [4, 5, 6, 7],
+            [8, 9, 10, 11],
+        ]
+
+        XCTAssertEqual(actual, expected)
+    }
+
     func test_init_arrayLiteral() {
         typealias Scalar = Double