Create README.md

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

numpy/new_matrix/README.md

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+# New matrices 
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## The goal
+
+Making a new matrix...
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+Using **import numpy as np** is the standard. 
+
+## Simple example -- new [np.zeros()](https://numpy.org/doc/stable/reference/generated/numpy.zeros.html)
+
+Define the size of your new matrix with a tuple, e.g.​
+
+```python
+M = numpy.zeros((DIM_0, DIM_1, DIM_2, …))​
+```
+
+### 1d
+
+```python
+import numpy as np
+
+M = np.zeros((2))
+print(M)
+```
+
+Output:
+
+```python
+[0. 0.]
+```
+
+### 2d
+
+```python
+import numpy as np
+
+M = np.zeros((2, 3))
+print(M)
+```
+
+Output:
+
+```python
+[[0. 0. 0.]
+ [0. 0. 0.]]
+```
+
+### 3d
+
+```python
+import numpy as np
+
+M = np.zeros((2, 3, 4))
+print(M)
+```
+
+Output:
+
+```python
+[[[0. 0. 0. 0.]
+  [0. 0. 0. 0.]
+  [0. 0. 0. 0.]]
+
+ [[0. 0. 0. 0.]
+  [0. 0. 0. 0.]
+  [0. 0. 0. 0.]]]
+```
+
+## Simple example -- recycle [np.zeros_like()](https://numpy.org/doc/stable/reference/generated/numpy.zeros_like.html)
+
+If you have a matrix with the same size ​you want then you can use zeros_like. This will also copy other properties like the data type.
+
+as a prototype use​
+
+N = numpy.zeros_like(M) ​
+
+```python
+import numpy as np
+
+M = np.zeros((2, 3, 4))
+
+N = np.zeros_like(M)
+print(N)
+```
+
+Output:
+
+```python
+[[[0. 0. 0. 0.]
+  [0. 0. 0. 0.]
+  [0. 0. 0. 0.]]
+
+ [[0. 0. 0. 0.]
+  [0. 0. 0. 0.]
+  [0. 0. 0. 0.]]]
+```
+
+## Remember unpacking
+
+{: .topic-optional}
+This is an optional topic!
+
+```python
+import numpy as np
+
+d = (3, 4)
+M = np.zeros((2, *d))
+
+print(M)
+```
+
+