Add directory for Pad protocol and extensions

Author: wigging

Sources/Numerix/Core/Pad.swift

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+/*
+Double extension to conform to Pad protocol.
+*/
+
+import Accelerate
+
+@_documentation(visibility: private)
+extension Double: Pad {
+    public static func pad(a: Matrix<Double>, value: Double) -> Matrix<Double> {
+        let m = vDSP_Length(a.columns)       // number of columns to copy
+        let n = vDSP_Length(a.rows)          // number of rows to copy
+        let ta = vDSP_Length(a.columns)      // number of columns in a
+        let tc = vDSP_Length(a.columns + 2)  // number of columns in c
+
+        let c = Matrix<Double>(rows: a.rows + 2, columns: a.columns + 2, fill: value)
+        vDSP_mmovD(a.buffer.baseAddress!, c.buffer.baseAddress! + (a.columns + 3), m, n, ta, tc)
+
+        return c
+    }
+}

Sources/Numerix/Pad/Double+Pad.swift

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+/*
+Float extension to conform to Pad protocol.
+*/
+
+import Accelerate
+
+@_documentation(visibility: private)
+extension Float: Pad {
+    public static func pad(a: Matrix<Float>, value: Float) -> Matrix<Float> {
+        let m = vDSP_Length(a.columns)       // number of columns to copy
+        let n = vDSP_Length(a.rows)          // number of rows to copy
+        let ta = vDSP_Length(a.columns)      // number of columns in a
+        let tc = vDSP_Length(a.columns + 2)  // number of columns in c
+
+        let c = Matrix<Float>(rows: a.rows + 2, columns: a.columns + 2, fill: value)
+        vDSP_mmov(a.buffer.baseAddress!, c.buffer.baseAddress! + (a.columns + 3), m, n, ta, tc)
+
+        return c
+    }
+}

Sources/Numerix/Pad/Float+Pad.swift

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+/*
+Matrix extension for Pad protocol.
+*/
+
+extension Matrix where Scalar: Pad, Scalar: Numeric {
+
+    /// Pad a matrix with a constant value.
+    ///
+    /// Create a padded matrix with zeros.
+    /// ```swift
+    /// let a: Matrix<Float> = [[1, 2],
+    ///                         [3, 4]]
+    /// let p = a.pad()
+    /// // The matrix p has values of
+    /// // 0 0 0 0
+    /// // 0 1 2 0
+    /// // 0 3 4 0
+    /// // 0 0 0 0
+    /// ```
+    /// Create a padded matrix using a value of 9.
+    /// ```swift
+    /// let a: Matrix<Float> = [[1, 2],
+    ///                         [3, 4]]
+    /// let p = a.pad(with: 9)
+    /// // The matrix p has values of
+    /// // 9 9 9 9
+    /// // 9 1 2 9
+    /// // 9 3 4 9
+    /// // 9 9 9 9
+    /// ```
+    ///
+    /// - Parameter value: The scalar value for padding the matrix. Default is 0.
+    /// - Returns: A padded matrix with zeros or some other value along its border.
+    public func pad(with value: Scalar = .zero) -> Matrix {
+        Scalar.pad(a: self, value: value)
+    }
+}

Sources/Numerix/Pad/Matrix+Pad.swift

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+/*
+Pad protocol.
+Inspired my the NumPy pad function https://numpy.org/doc/stable/reference/generated/numpy.pad.html
+*/
+
+import Accelerate
+
+@_documentation(visibility: private)
+public protocol Pad {
+    static func pad(a: Matrix<Self>, value: Self) -> Matrix<Self>
+}