This application is only for educational scope.
The usage is very simple.
You have to fill the matrix tensor (symmetric) and then to press the "Submit" button.
You can immediately find the principal stresses, the Shear max (radius of maximum circle) and the ideal stress according to the von Mises theory.
Also you can find the abscissas centres and the diameters of the Mohr's Circles.
At the bottom you can view the three Mohr's Circles.

The algorithm is:

Consider a full 3x3 "stress" matrix (symmetric)

The principal stresses are the S eigenvalues and the associated eigenvectors determin the principal directions.
Let:

The eigenvalues are the solutions of the following secolar equation:

Order the solutions such that:

Centres (C) and diameters (D) of Mohr's circle are:

The ideal tension according von Mises is: