Added mish layer doc opset (#1149)

* Added mish layer doc opset

* Refactoring mish spec

* Update mish spec

* Change output description of Mish layer

* Fix Mish according to review

* Refactoring Mish and GELU spec according to code review

* Update formula for ops in spec

* Refactoring spec text

* Update Mish opset

* Change Mish version from 1 to 4

* Sort opset4

Co-authored-by: Your Name <you@example.com>

docs/ops/activation/GELU_2.md

@@ -15,13 +15,15 @@ Gelu(x)=x*Φ(x), where Φ(x) is the Cumulative Distribution Function for Gaussia
 The following equivalent combination is recognized and fused into single Gelu op: 
 
 \f[
-    Gelu(x) = 0.5*x*(1 + erf((x) / sqrt(2) )
+    Gelu(x) = 0.5*x*(1.0 + erf((x) / \sqrt{2})
 \f]
 
-Similarly, the following Gelu approximation (typical for the TensorFlow*) is  recognized and fused into single Gelu op
+Similarly, the following Gelu approximation (typical for the TensorFlow*) is recognized and fused into single Gelu op 
+
 \f[
-    Gelu(x) \approx  0.5*x*(1 + tanh((sqrt(2/pi)) * (x + 0.044715 * x ^ 3))
+    Gelu(x) \approx 0.5x(1.0 + tanh(\sqrt{2.0/pi} * (x + 0.044715 * x ^ 3))
 \f]
+
 **Inputs**:
 
 *   **1**: Multidimensional input tensor. Required.

docs/ops/activation/Mish_4.md

@@ -0,0 +1,50 @@
+## Mish <a name="Mish"></a>
+
+**Versioned name**: *Mish-4*
+
+**Category**: *Activation*
+
+**Short description**: Mish is a Self Regularized Non-Monotonic Neural Activation Function.
+
+**Detailed description**: Mish is a self regularized non-monotonic neural activation function proposed in the [article](https://arxiv.org/abs/1908.08681).
+
+**Attributes**: operation has no attributes.
+
+**Inputs**:
+
+*   **1**: Input tensor *x* of any floating point type T. Required.
+
+**Outputs**:
+
+*   **1**: Floating point tensor with shape and type matching the input tensor. Required.
+
+**Types**
+
+* *T*: any floating point type.
+
+**Mathematical Formulation**
+
+   For each element from the input tensor calculates corresponding
+    element in the output tensor with the following formula:
+    \f[
+    Mish(x) = x*tanh(ln(1.0+e^{x}))
+    \f]
+
+**Examples**
+
+```xml
+<layer ... type="Mish">
+    <input>
+        <port id="0">
+            <dim>256</dim>
+            <dim>56</dim>
+        </port>
+    </input>
+    <output>
+        <port id="3">
+            <dim>256</dim>
+            <dim>56</dim>
+        </port>
+    </output>
+</layer>
+```

docs/ops/opset4.md

@@ -77,6 +77,7 @@ declared in `namespace opset4`.
 * [MaxPool](pooling/MaxPool_1.md)
 * [Maximum](arithmetic/Maximum_1.md)
 * [Minimum](arithmetic/Minimum_1.md)
+* [Mish](activation/Mish_4.md)
 * [Mod](arithmetic/Mod_1.md)
 * [MVN](normalization/MVN_1.md)
 * [Multiply](arithmetic/Multiply_1.md)