OKID errors for non-square systems

In the notebook here
https://github.com/dylewsky/Data_Driven_Science_Python_Demos/blob/master/CH09/CH09_SEC03_ERA_OKID.ipynb
OKID errors if the system is not square, i.e., if `q != p`
The error happens in the indexing here
```
for i in range(LL):
        Ybar1[:,:,i] = Ybar[:,QQ+(QQ+PP)*i : QQ+(QQ+PP)*i+QQ]
        Ybar2[:,:,i] = Ybar[:,QQ+(QQ+PP)*i+QQ : QQ+(QQ+PP)*(i+1)]
```