pymc.backends.base.MultiTrace — PyMC 5.22.0 documentation (original) (raw)

class pymc.backends.base.MultiTrace(straces)[source]#

Main interface for accessing values from MCMC results.

The core method to select values is get_values. The method to select sampler statistics is get_sampler_stats. Both kinds of values can also be accessed by indexing the MultiTrace object. Indexing can behave in four ways:

1. Indexing with a variable or variable name (str) returns all values for that variable, combining values for all chains.
   Slicing after the variable name can be used to burn and thin the samples.

   trace[varname, 1000:]
   For convenience during interactive use, values can also be accessed using the variable as an attribute.

2. Indexing with an integer returns a dictionary with values for each variable at the given index (corresponding to a single sampling iteration).
3. Slicing with a range returns a new trace with the number of draws corresponding to the range.
4. Indexing with the name of a sampler statistic that is not also the name of a variable returns those values from all chains. If there is more than one sampler that provides that statistic, the values are concatenated along a new axis.

For any methods that require a single trace (e.g., taking the length of the MultiTrace instance, which returns the number of draws), the trace with the highest chain number is always used.

Attributes:

nchains: int

Number of chains in the MultiTrace.

chains: `List[int]`

List of chain indices

report: str

Report on the sampling process.

varnames: `List[str]`

List of variable names in the trace(s)

Methods

Attributes