Results 3 issues of David

As pointed out by a user in the Issues (#68), the demo2.py had a tiny problem with the initialization values in List[] that could be easily fixed. I had the...

Solving the issues that I've found in the test script. ![Screenshot 2021-09-02 at 12 48 52](https://user-images.githubusercontent.com/47969361/131830977-3d039ee2-8e68-4e22-bd55-618c2e08a51a.png)

2 PendingDeprecationWarning: the matrix subclass is not the recommended way to represent matrices or deal with linear algebra.