Create README.md

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

pytorch/optimizer_special/README.md

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+# How to take advantage of an optimizer for your non-Pytorch project
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## The goal
+
+Pytorch provides you with optimizer. Their job is to update your parameter (e.g. weights) with a gradient. How can we use it for our own stimulation, without using the rest of PyTorch? 
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+In a first step we build a dummy torch layer from a **nn.Module**. It contains a registered  parameter: (here it is the weight). 
+
+## Dummy torch layer
+
+```python
+import torch
+
+my_module: torch.nn.Module = torch.nn.Module()
+my_parameter: torch.nn.Parameter = torch.nn.Parameter(
+    torch.ones((10, 5)), requires_grad=True
+)
+my_module.register_parameter("w", my_parameter)
+
+
+if my_module._parameters["w"] is None:
+    raise Exception("Parameter w is missing.")
+else:
+    my_gradient = torch.zeros_like(my_module._parameters["w"])
+```
+
+The parameter consists of data
+
+```python
+my_module._parameters["w"].data
+```
+
+and the gradient
+
+```python
+my_module._parameters["w"].grad
+```
+
+We can interface the gradient and the data of the parameter via **.grad** and **.data**. It is important both are **torch.Tensor** elements and have the same dtype (Probably the dtype is not allowed to change but I didn't tested that.). 
+
+## The optimizer
+
+Now we can connect the parameters to an optimizer . Here I will use Adam: 
+
+```python
+optimizer = torch.optim.Adam(my_module.parameters())
+```
+
+If we want to use the power of the optimizer we fill our momentary gradient and the old weights into the parameter **.grad** and **.data** and call
+
+```python
+optimizer.step()
+```
+
+Now we can read the optimized weights from **.data** and put them into our non-PyTorch network. I addition we can add a lr scheduler too. 
+
+Notes:
+
+* Don't replace the my_module._parameters["w"] with a new parameter object. Then the optimizer looses the contact to the parameter. Only use .data and .grad !
+* Don't use this for different parameters. Let's say you have two layers. Then you need to create TWO fake layers and TWO optimizers (and TWO lr_scheduler). An optimizer has internal memory thus it should only deal with it's parameter. 
+* You need to tell the optimizier if you want to use old parameter - update (default) or  old parameter + update (maximize=True)
+