Added support for the 'expm1' op and its VJP. (#146)

Author: eaplatanios

Sources/TensorFlow/Operators/Math.swift

@@ -569,6 +569,21 @@ internal func _vjpExp<T: TensorFlowFloatingPoint>(
     return (value, { v in value * v })
 }
 
+/// Computes the exponential of `x - 1` element-wise.
+@inlinable
+@differentiable(vjp: _vjpExpm1)
+public func expm1<T: TensorFlowFloatingPoint>(_ x: Tensor<T>) -> Tensor<T> {
+    Raw.expm1(x)
+}
+
+@inlinable
+internal func _vjpExpm1<T: TensorFlowFloatingPoint>(
+    _ x: Tensor<T>
+) -> (Tensor<T>, (Tensor<T>) -> Tensor<T>) {
+    let y = expm1(x)
+    return (y, { v in v * y })
+}
+
 /// Returns the values of the specified tensor rounded to the nearest integer, element-wise.
 @inlinable
 @differentiable(vjp: _vjpRound)

Tests/TensorFlowTests/OperatorTests/MathTests.swift

@@ -22,6 +22,12 @@ final class MathOperatorTests: XCTestCase {
         assertEqual(y, log(1 + x), accuracy: 0.0001)
     }
 
+    func testExpm1() {
+        let x = Tensor<Float>([[1, 2, 3, 4, 5], [1, 2, 3, 4, 5]])
+        let y = expm1(x)
+        assertEqual(y, exp(x - 1), accuracy: 0.0001)
+    }
+
     func testSign() {
         let x = Tensor<Float>([[1, 2, -3, 4, 5], [1, 2, 3, 4, -5]])
         let y = sign(x)
@@ -224,6 +230,7 @@ final class MathOperatorTests: XCTestCase {
 
     static var allTests = [
         ("testLog1p", testLog1p),
+        ("testExpm1", testExpm1),
         ("testSign", testSign),
         ("testReduction", testReduction),
         ("testArgmax", testArgmax),