The background is discussed in 2. Identifying feasible assignments of
Ordering matrices to bordered lower triangular form with minimal border width.
The code here is derived from:
https://github.com/baharev/sdopt-tearing/blob/master/sympy_tree.py
However, sympy_tree.py is concerned with binary expression trees coming
from Modelica and
generating output for
AMPL.
The solvable.py is only concerned with expression trees coming from, and
going to SymPy.
The caveats mentioned in the last two paragraphs of
2.2. Identifying numerically troublesome assignments in
Ordering matrices to bordered lower triangular form with minimal border width
do apply!
Of course, the long-term goal is to merge the code back into sdopt-tearing.