Terms of Reference#
Background#
This document lays out terms of reference for TJPCov developers and contributors in the wider MCP and LSST DESC context.
Scope#
TJPCov provides a set of APIs for calculation of covariance (and cross-covariance) matrices (or other descriptions of measurement uncertainty as required) for all main canonical large scale structure cosmological probes in DESC:
weak lensing shear
galaxy clustering
galaxy clusters clustering
galaxy clusters number counts
It provides flexibility in how its functionality is accessed:
it is called from TXPipe and APIs are designed to work with TXPipe
it can be called as a standalone library
it can be called from the command line through driver routines
Interface support is as follows:
Public APIs are maintained in Python
Documentation should be maintained in the main README, readthedocs, and the benchmarks folder.
Command-line driver routines are maintained in the bin folder
Examples will be maintained in a separate repository. [AS?]
In the basic model, covariance matrices are factorised as follows:
Disconnected part of the Gaussian covariance matrix
Connected part of the Gaussian covariance matrix arising from mode coupling
Additional covariance due to super-survey modes
External libraries:
TJPCov aims to implement basic functionality internally but supports an external back-end for versatility and cross-checking
External back-ends can be linked as external libraries (on top of a thin wrapper inside TJPCov), but must be interfaced via pure python (i.e., the external back-end must implement a python wrapper as a precondition to be integrated into TJPCov)
Boundaries of TJPCov:
TJPCov does not support the calculation of covariance matrices that are not covariant with the main large-scale structure probes (i.e., supernovae luminosity distance)
TJPCov performs theoretical computations of the covariance matrix given survey properties and assumed cosmology. It does not perform calculations on the data, e.g., various bootstrap techniques
In general, TJPCov does not support covariance arising from systematic effects although exceptions could be made on an as-needed basis (i.e., we provide a covariance matrix as observed by a perfect instrument with no galactic foregrounds, etc.)