Create README.md

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

numpy_mat_files/README.md

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+# Numpy: Dealing with Matlab files
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## The goal
+We want to read and write Matlab files under Python.
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+Reminder: Learning Python as Matlab user
+Please read [NumPy for MATLAB users](https://numpy.org/doc/stable/user/numpy-for-matlab-users.html)
+
+## Mat files under Python
+
+### MATLAB <= 7.2 format mat files
+
+This is a job for [scipy.io](https://docs.scipy.org/doc/scipy/reference/io.html#module-scipy.io)
+
+| | |
+| ------------- |-------------|
+|[loadmat](https://docs.scipy.org/doc/scipy/reference/generated/scipy.io.loadmat.html#scipy.io.loadmat)(file_name[, mdict, appendmat])|	Load MATLAB file. |
+|[savemat](https://docs.scipy.org/doc/scipy/reference/generated/scipy.io.savemat.html#scipy.io.savemat)(file_name, mdict[, appendmat, …])|	Save a dictionary of names and arrays into a MATLAB-style .mat file. |
+|[whosmat](https://docs.scipy.org/doc/scipy/reference/generated/scipy.io.whosmat.html#scipy.io.whosmat)(file_name[, appendmat])|	List variables inside a MATLAB file. |
+
+#### Read
+Under Matlab we create a test file
+
+```matlab
+>> A = rand(10,100);
+>> save -v7 Test_1.mat A
+```
+
+Under Python we look into the file for information:
+```python
+import scipy.io as sio
+
+Info = sio.whosmat("Test_1.mat")
+print(Info) # --> [('A', (10, 100), 'double')]
+```
+
+And we can read the data: 
+
+```python
+import numpy as np
+import scipy.io as sio
+
+mat_data = sio.loadmat("Test_1.mat")
+
+print(
+    mat_data.keys()
+)  # -> dict_keys(['__header__', '__version__', '__globals__', 'A'])
+
+a = mat_data["A"]
+print(type(a))  # --> <class 'numpy.ndarray'>
+print(a.dtype)  # --> float64
+print(a.shape)  # --> (10, 100)
+```
+
+#### Write
+
+Under Python we generate a .mat file:
+
+```python
+import numpy as np
+import scipy.io as sio
+
+myrng = np.random.default_rng()
+
+A: np.ndarray = myrng.random((10, 100), dtype=np.float64)
+B: str = "Hellp world!"
+mdic = {"A": A, "ImportantMessage": B}
+sio.savemat("Test_2.mat", mdic)
+```
+
+And read it in under Matlab:
+
+```matlab
+>> load Test_2.mat
+>> whos
+  Name                   Size             Bytes  Class     Attributes
+
+  A                     10x100             8000  double              
+  ImportantMessage       1x12                24  char                
+
+>> ImportantMessage
+
+ImportantMessage =
+
+    'Hellp world!'
+```