Added support for the 'log1p' op and its VJP. (#145)

Author: eaplatanios

Sources/TensorFlow/Operators/Math.swift

@@ -408,6 +408,20 @@ internal func _vjpLog<T: TensorFlowFloatingPoint>(
     return (log(x), { v in v / x })
 }
 
+/// Computes the logarithm of `1 + x` element-wise.
+@inlinable
+@differentiable(vjp: _vjpLog1p)
+public func log1p<T: TensorFlowFloatingPoint>(_ x: Tensor<T>) -> Tensor<T> {
+    Raw.log1p(x)
+}
+
+@inlinable
+func _vjpLog1p<T: TensorFlowFloatingPoint>(
+    _ x: Tensor<T>
+) -> (Tensor<T>, (Tensor<T>) -> Tensor<T>) {
+    (log1p(x), { v in Raw.xdivy(v, 1 + x) })
+}
+
 /// Computes `sin` of the specified tensor element-wise.
 @inlinable
 @differentiable(vjp: _vjpSin(_:) where T: TensorFlowFloatingPoint)

Tests/TensorFlowTests/OperatorTests/MathTests.swift

@@ -16,6 +16,12 @@ import XCTest
 @testable import TensorFlow
 
 final class MathOperatorTests: XCTestCase {
+    func testLog1p() {
+        let x = Tensor<Float>([[1, 2, 3, 4, 5], [1, 2, 3, 4, 5]])
+        let y = log1p(x)
+        assertEqual(y, log(1 + x), accuracy: 0.0001)
+    }
+
     func testSign() {
         let x = Tensor<Float>([[1, 2, -3, 4, 5], [1, 2, 3, 4, -5]])
         let y = sign(x)
@@ -217,6 +223,7 @@ final class MathOperatorTests: XCTestCase {
 	}
 
     static var allTests = [
+        ("testLog1p", testLog1p),
         ("testSign", testSign),
         ("testReduction", testReduction),
         ("testArgmax", testArgmax),