Softmax revise (#3249)

* Update spec

* add default value to axis parameter

* add test for default axis value

* style apply

* remove default axis unit-test

* add node validation check for negative axis

* create type prop tests for default and negative axis values

* add softmax type_prop file to CMakeLists

* style-apply

* fix axis condition

* remove unnecessary node validation check

* rename prop_type test

* style-apply

docs/ops/activation/SoftMax_1.md

@@ -2,7 +2,7 @@
 
 **Versioned name**: *SoftMax-1*
 
-**Category**: *Activation*
+**Category**: *Activation function*
 
 **Short description**: [Reference](https://github.com/Kulbear/deep-learning-nano-foundation/wiki/ReLU-and-Softmax-Activation-Functions#softmax)
 
@@ -18,6 +18,12 @@
   * **Default value**: 1
   * **Required**: *no*
 
+**Mathematical Formulation**
+
+\f[
+y_{c} = \frac{e^{Z_{c}}}{\sum_{d=1}^{C}e^{Z_{d}}}
+\f]
+where \f$C\f$ is a size of tensor along *axis* dimension.
 
 **Inputs**:
 
@@ -27,13 +33,6 @@
 
 *   **1**: The resulting tensor of the same shape and type as input tensor.
 
-**Detailed description**
-
-\f[
-y_{c} = \frac{e^{Z_{c}}}{\sum_{d=1}^{C}e^{Z_{d}}}
-\f]
-where \f$C\f$ is a size of tensor along *axis* dimension.
-
 **Example**
 
 ```xml

ngraph/core/include/ngraph/op/softmax.hpp

@@ -41,7 +41,7 @@ namespace ngraph
                 ///
                 /// Output `[d0, ...]`
                 ///
-                Softmax(const Output<Node>& arg, const size_t axis);
+                Softmax(const Output<Node>& arg, const size_t axis = 1);
 
                 bool visit_attributes(AttributeVisitor& visitor) override;
                 void validate_and_infer_types() override;

ngraph/test/CMakeLists.txt

@@ -172,6 +172,7 @@ set(SRC
     type_prop/select.cpp
     type_prop/shape_of.cpp
     type_prop/shuffle_channels.cpp
+    type_prop/softmax.cpp
     type_prop/softplus.cpp
     type_prop/space_to_batch.cpp
     type_prop/space_to_depth.cpp

ngraph/test/type_prop/softmax.cpp

@@ -0,0 +1,37 @@
+//*****************************************************************************
+// Copyright 2017-2020 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//*****************************************************************************
+
+#include "gtest/gtest.h"
+#include "ngraph/ngraph.hpp"
+
+using namespace std;
+using namespace ngraph;
+
+TEST(type_prop, softmax_default_axis)
+{
+    const Shape arg_shape{2, 3};
+    auto arg = make_shared<op::Parameter>(element::f32, arg_shape);
+    auto sm = make_shared<op::v1::Softmax>(arg);
+    ASSERT_EQ(sm->get_axis(), 1);
+}
+
+TEST(type_prop, softmax_out_of_bound_axis)
+{
+    const Shape arg_shape{2, 3};
+    auto arg = make_shared<op::Parameter>(element::f32, arg_shape);
+    // axis cannot be a negative number
+    ASSERT_THROW(make_shared<op::v1::Softmax>(arg, -1), ngraph::NodeValidationFailure);
+}