Common Issues and Solutions

Not all models will simulate flawlessly. Some problems may arise upon the initialization of the model, or during the simulation itself. Below, the most common exceptions and/or issues are shown.

AssertionError: Can only add BaseBlock (subclass) instances to a CBD

This error is thrown whenever you try adding a block using the pyCBD.Core.CBD.addBlock() function if that block does not inherit from the pyCBD.Core.BaseBlock class.

NotImplementedError: BaseBlock has nothing to compute

When invalidly inheriting a pyCBD.Core.BaseBlock, this error may occur. It is a consequence of not overwriting the pyCBD.Core.BaseBlock.compute() method.

ValueError: Specified object/influencer/dependent is not member of this graph

This issue is indicative of an error in the dependency graph construction. Usually, this is due to an invalid connection between blocks. Make sure to always connect blocks that have been added to the CBD model. I.e. always call pyCBD.Core.CBD.addBlock() before any pyCBD.Core.CBD.addConnection() that includes the same block.

KeyError: ‘X’

This exception occurs if X cannot be found. Make sure that X is actually a block or a port in your model.

Cannot solve non-linear algebraic loop.

The internal solver of the CBD simulator is a simple Gaussian-Jordan Linear solver (see pyCBD.solver.GaussianJordanLinearSolver) that uses row reduction to solve the algebraic loop. However, if this loop represents a non-linear system, the solver cannot handle this. Make use of a pyCBD.lib.std.DelayBlock to actively “break” the loop.

Hint: Internally, the pyCBD.lib.std.DerivatorBlock and the pyCBD.lib.std.IntegratorBlock make use of a pyCBD.lib.std.DelayBlock, hence they can be used to solve the issue.

Warning: did not add this block as it has the same name X as an already existing block

A warning that’s generated by the pyCBD.Core.CBD.addBlock() method if it shares the same name as an already existing block. This is meant to ensure uniqueness of names.

ImportError: cannot import name ‘Clock’ from partially initialized module ‘pyCBD.lib.std’

Before importing the standard library, it is important to also import the pyCBD.Core module. This will solve the circular dependency and dissipate the error.