Especially circuits with many resistors in some cases can not be simplified through the parallel or series connection of resistors.
The problem solves only the star-delta-transform.
With the help of this transform at least a circuit part of 3 resistors can be so converted, that then a parallel or series connection of 2 adjacent resistors is possible.
To come to a solution for the entire circuit, you may must apply the transform at different circuit parts and in different directions.
The first script calculates the delta-circuit from the star-circuit.
The second script calculates the star-circuit from the delta-circuit.