Why does the output of a discrete transfer function goes NaN?

My simulink model has a discrete transfer function block.The numerator and the denominator are given externally because their coefficients change as the simulation runs.What are the possible reasons for the output of the discrete transfer function to go NaN?What are the possible soultions to solve the same?

[Rahul Shinde]

Hello there, did you happen to find any solution to your problem?

I am kind of facing the same issue for one of models (which is a derived version).

The former version works fine but the derived version generates a "nan" at the DTF output.

[Walter Roberson]

You have infinity or negative infinity in the input signal, and you do not happen to have the situation where all non-zero coefficients appear only in even powers.

For example negative infinity and coefficients [1 1 1] would be 1*(-inf)^2 + 1*(-inf) + 1 which would be (inf) + (-inf) + 1 and inf - inf is nan.

[Rahul Shinde]

Many thanks for your response @Walter Roberson. After your hints I was able to focus & identify the issue in my model.

Good day.