Energy-based truncator in ROM code leading to divide-by-zero error

[ikalash]

It looks like the EnergyBasedTruncater in norma-opinf is leading to a divide-by-zero error in some cases. The problem can be reproduced by running:

https://github.com/sandialabs/Norma.jl/blob/main/examples/ahead/single/clamped/dynamic-opinf-fom/make_op_inf_models.py

with this line uncommented: https://github.com/sandialabs/Norma.jl/blob/main/examples/ahead/single/clamped/dynamic-opinf-fom/make_op_inf_models.py#L28 . The error looks like:

/usr/local/lib/python3.9/site-packages/romtools/vector_space/utils/truncater.py:154: RuntimeWarning: invalid value encountered in divide
  energy = np.cumsum(singular_values**2)/np.sum(singular_values**2)

To reproduce, you first need to run https://github.com/sandialabs/Norma.jl/blob/main/examples/ahead/single/clamped/dynamic-opinf-fom/clamped.yaml . I suggest changing final time to 5.0e-5 so that the problem doesn't take as long to run.