[LPT] Add operation was added

docs/low_precision_transformations/transformations/step3_main/arithmetic/add.md

@@ -1 +1,33 @@
-# OpenVINO™ Low Precision Transformations: AddTransformation {#openvino_docs_IE_DG_lpt_AddTransformation}
+# OpenVINO™ Low Precision Transformations: AddTransformation {#openvino_docs_IE_DG_lpt_AddTransformation}
+
+The transformation propagates dequantization operations from one input branch to another and below `Add` operation. One or both branches can be quantized. As result, one `Add` operation input branch is in low precision without dequantization operations, another input branch is in original precision with updated dequantization operations.
+
+During inference dequantization operations from another input will be fused in previous operation, for example in `Convolution` or `FakeQuantize`. This approach allows to infer `Add` operation in the most optimal way.
+
+## Subgraph before transformation
+The subgraph with quantized `Add` operation before transformation:
+
+\f[
+y_{ch,i}=(scale1_{ch} * (x1_{ch,i} - shift1_{ch})) + (scale2_{ch} * (x2_{ch,i} - shift2_{ch}))
+\f]
+
+![Add before](img/add.common.png)
+
+## Subgraph after transformation
+The subgraph with `Add` operation after the transformation:
+
+\f[
+y_{ch,i}=scale2_{ch} * (scale1_{ch}' * (x1_{ch,i} - shift1_{ch}') + x2_{ch,i})
+\f]
+
+where:
+
+\f[
+scale1_{ch}' = scale1_{ch} / scale2_{ch}
+\f]
+
+\f[
+shift1_{ch}' = shift1_{ch} + scale2_{ch} * shift2_{ch} / scale1_{ch}
+\f]
+
+![Add before](img/add.transformed.png)