You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
I am trying to use BXA to compare two models on an XMM-Newton data set and I have issues of convergence, probably due to some parameter degeneracy, even if models are not very complex:
constant * TBabs * pow (This one converged in an hour or so)
constant * TBabs * pcfabs * pow
This last one has been running for more than one day and it does not look to be converging.
The warning is:
/pyenv/versions/3.8.2/lib/python3.8/site-packages/ultranest/integrator.py:1632: UserWarning: Sampling from region seems inefficient (0/40 accepted in iteration 2500). To improve efficiency, modify the transformation so that the current live points (stored for you in BXA-pcfabs/extra/sampling-stuck-it%d.csv) are ellipsoidal, or use a stepsampler, or set frac_remain to a lower number (e.g., 0.5) to terminate earlier.
warnings.warn(warning_message)
I have already put frac_reami=0.5 in my parameters, but I do not understand well this thing of ellipsoids...
Do you have some suggestions to increase efficiency ?
Making a corner plot of the CSV file, gives me this:
Most of the plots look ellipsoidal. However, in the first panel of the second row, it seems there is a inverted L-shape.
This can be inefficient to sample with the MLFriends algorithm. Your choices are to:
try to reparameterize so that it is easier to sample
to use a different algorithm (for example, a step sampler), to continue.
If you know that some regions of the parameter space are unreasonable, update the prior.
Looking at the two arms of this L:
The left half tightly constrains the first parameter to a narrow range, while the right allows it to be wider.
I don't know what your parameters mean, but I want to give you an example of a beneficial reparametrization.
Lets say, the first and third parameter are each a normalisation of components, each with a log-uniform prior. The data constrain to first order the sum of these components. Therefore, a L shape appears, where at least one of the two component normalisations has to exceed a threshold. To remove the L shape, one can use a total normalisation parameter, and a relative normalisation parameter (e.g., the ratio between the two components, or similar).
Hi Johannes,
I am trying to use BXA to compare two models on an XMM-Newton data set and I have issues of convergence, probably due to some parameter degeneracy, even if models are not very complex:
constant * TBabs * pow (This one converged in an hour or so)
constant * TBabs * pcfabs * pow
This last one has been running for more than one day and it does not look to be converging.
The warning is:
/pyenv/versions/3.8.2/lib/python3.8/site-packages/ultranest/integrator.py:1632: UserWarning: Sampling from region seems inefficient (0/40 accepted in iteration 2500). To improve efficiency, modify the transformation so that the current live points (stored for you in BXA-pcfabs/extra/sampling-stuck-it%d.csv) are ellipsoidal, or use a stepsampler, or set frac_remain to a lower number (e.g., 0.5) to terminate earlier.
warnings.warn(warning_message)
I have already put frac_reami=0.5 in my parameters, but I do not understand well this thing of ellipsoids...
Do you have some suggestions to increase efficiency ?
You find attached some files from the run
debug.log
sampling-stuck-it%d.csv
The WIP notebook is in
https://gitlab.astro.unige.ch/xmm-newton-workflows/0862410301
which uses the call to BXA in
https://gitlab.astro.unige.ch/ferrigno/pysas/-/blob/master/pyxmmsas/__init__.py#L420
The text was updated successfully, but these errors were encountered: