Add L1 & L2 losses and respective tests (#231)

Author: Shashi456

Sources/TensorFlow/Loss.swift

@@ -12,6 +12,30 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+/// Returns the L1 loss between predictions and labels.
+///
+/// - Parameters:
+///   - predicted: Predicted outputs from a neural network.
+///   - labels: Expected values, i.e. targets, that correspond to the correct output.
+@differentiable(wrt: predicted)
+public func l1Loss<Scalar: TensorFlowFloatingPoint>(
+    predicted: Tensor<Scalar>, expected: Tensor<Scalar>
+) -> Tensor<Scalar> {
+    return abs(expected - predicted).sum()
+}
+
+/// Returns the L2 loss between predictions and labels.
+///
+/// - Parameters:
+///   - predicted: Predicted outputs from a neural network.
+///   - labels: Expected values, i.e. targets, that correspond to the correct output.
+@differentiable(wrt: predicted)
+public func l2Loss<Scalar: TensorFlowFloatingPoint>(
+    predicted: Tensor<Scalar>, expected: Tensor<Scalar>
+) -> Tensor<Scalar> {
+    return (expected - predicted).squared().sum()
+}
+
 /// Returns the mean squared error between predictions and labels.
 ///
 /// - Parameters:

Tests/TensorFlowTests/LossTests.swift

@@ -16,6 +16,22 @@ import XCTest
 @testable import TensorFlow
 
 final class LossTests: XCTestCase {
+    func testL1Loss() {
+        let predicted = Tensor<Float>([1, 2, 3, 4])
+        let expected = Tensor<Float>([0.1, 0.2, 0.3, 0.4])
+        let loss = l1Loss(predicted: predicted, expected: expected)
+        let expectedLoss: Float = 9.0
+        assertElementsEqual(expected: Tensor(expectedLoss), actual: loss)
+    }
+
+    func testL2Loss() {
+        let predicted = Tensor<Float>([1, 2, 3, 4])
+        let expected = Tensor<Float>([0.5, 1.5, 2.5, 3.5])
+        let loss = l2Loss(predicted: predicted, expected: expected)
+        let expectedLoss: Float = 1.0
+        assertElementsEqual(expected: Tensor(expectedLoss), actual: loss)
+    }
+
     func testMeanSquaredErrorLoss() {
         let predicted = Tensor<Float>(shape: [2, 4], scalars: [1, 2, 3, 4, 5, 6, 7, 8])
         let expected = Tensor<Float>(
@@ -210,6 +226,8 @@ final class LossTests: XCTestCase {
     }
 
     static var allTests = [
+        ("testL1Loss", testL1Loss),
+        ("testL2Loss", testL2Loss),
         ("testMeanSquaredErrorLoss", testMeanSquaredErrorLoss),
         ("testMeanSquaredErrorGrad", testMeanSquaredErrorGrad),
         ("testMeanSquaredLogarithmicError", testMeanSquaredLogarithmicError),