Bugfix for the metal elu kernel. (huggingface#2490)

* Bugfix for the metal elu kernel.

* Add a test.

candle-core/tests/tensor_tests.rs

@@ -193,6 +193,19 @@ fn unary_op(device: &Device) -> Result<()> {
         tensor.sign()?.to_vec1::<f32>()?,
         [-1., -1., -1., 0., 0., 1., 1., 1., 1.]
     );
+    let tensor = Tensor::new(&[-1.0f32, 0., -2., 3.], device)?;
+    let y = tensor.elu(2.)?;
+    assert_eq!(
+        test_utils::to_vec1_round(&y, 4)?,
+        [-1.2642, 0.0000, -1.7293, 3.0000]
+    );
+    // This test failed on metal prior to the following PR:
+    // https://github.com/huggingface/candle/pull/2490
+    let y = tensor.reshape((2, 2))?.t()?.elu(2.)?.flatten_all()?;
+    assert_eq!(
+        test_utils::to_vec1_round(&y, 4)?,
+        [-1.2642, -1.7293, 0.0000, 3.0000]
+    );
     Ok(())
 }
 

candle-metal-kernels/src/affine.metal

@@ -105,7 +105,7 @@ kernel void FN_NAME##_strided( \
         return; \
     } \
     const TYPENAME x = input[get_strided_index(id, num_dims, dims, strides)]; \
-    output[id] = TYPENAME((x > 0)?x: mul * exp(x - 1)); \
+    output[id] = TYPENAME((x > 0)?x: mul * (exp(x) - 1)); \
 } \