Covariance matrices

Covariance manages multi-group relative covariance matrices obtained from ENDF-6 nuclear-data evaluations. The class can coordinate processing with SANDY and NJOY or read existing ERRORR output from a working directory. With database=True, cwd is treated as the root of a structured library/grid tree. With database=False, covariance and ENDF files are read or generated directly in cwd.

Core inputs include:

  • ZAID;

  • temperature;

  • energy-group structure and its name;

  • evaluated nuclear-data library;

  • working or database directory;

  • resonance-processing options.

The parsed covariance matrices are organized by ERRORR MF section and MT pair. The get method extracts a requested covariance block and can return either the underlying pandas representation or a NumPy array. The MF argument is required, keyword-only, and must identify the section explicitly, either as an integer such as MF=33 or as an ERRORR key such as MF="errorr35".

from pyNDUS import Covariance

cov = Covariance(
    zaid=922350,
    temperature=300,
    group_structure=energy_grid,
    egridname="custom",
    lib="endfb_80",
    cwd="covariance_database",
)

c_18_102 = cov.get((18, 102), MF="errorr33", to_numpy=True)

NJOY availability, evaluated-data access, and the exact SANDY interface are external requirements and should be verified in the target environment.