[ONNX] Non-linear ops (#1864)

* [ONNX] Non-linear ops

* Style check

src/ngraph/frontend/onnx_import/op/prelu.cpp

@@ -20,16 +20,18 @@
 
 #include "ngraph/node.hpp"
 #include "ngraph/node_vector.hpp"
-
+#include "ngraph/op/add.hpp"
 #include "ngraph/op/broadcast.hpp"
-#include "ngraph/op/maximum.hpp"
+#include "ngraph/op/constant.hpp"
+#include "ngraph/op/convert.hpp"
+#include "ngraph/op/greater.hpp"
+#include "ngraph/op/less.hpp"
 #include "ngraph/op/multiply.hpp"
 #include "ngraph/op/reshape.hpp"
 
 #include "core/node.hpp"
-#include "utils/broadcasting.hpp"
-
 #include "prelu.hpp"
+#include "utils/broadcasting.hpp"
 
 namespace ngraph
 {
@@ -54,13 +56,33 @@ namespace ngraph
                         auto index = std::distance(std::begin(data_shape), it);
                         slope = make_broadcast_node(slope, data->get_shape(), index);
                     }
-                    else
+                    else if (data_shape != slope_shape)
                     {
                         auto params = numpy_style_broadcast_for_binary_operation(slope, data);
                         slope = params.at(0);
                     }
 
-                    return {std::make_shared<ngraph::op::Maximum>(data * slope, data)};
+                    // x <  0 => f(x) = x * slope
+                    // x >= 0 => f(x) = x
+
+                    std::shared_ptr<ngraph::Node> zero_node =
+                        std::make_shared<ngraph::op::Constant>(
+                            data->get_element_type(), ngraph::Shape{}, std::vector<double>{0});
+                    zero_node = make_broadcast_node(zero_node, data->get_shape());
+
+                    std::shared_ptr<ngraph::Node> negative_map =
+                        std::make_shared<ngraph::op::Convert>(
+                            std::make_shared<ngraph::op::Less>(data, zero_node),
+                            data->get_element_type());
+
+                    std::shared_ptr<ngraph::Node> positive_map =
+                        std::make_shared<ngraph::op::Convert>(
+                            std::make_shared<ngraph::op::Greater>(data, zero_node),
+                            data->get_element_type());
+
+                    slope = negative_map * slope + positive_map;
+
+                    return {data * slope};
                 }
 
             } // namespace set_1