GLaSS

Background

statement: This is the Generalised Lensing and Shear Spectra (Glass) code. It is a module for Cosmosis. See https://bitbucket.org/joezuntz/cosmosis/wiki/Home for more detials. Please contact Peter Taylor (peterllewlyntaylor at gmail dot com) if there are problems. If you use GLaSS please remember to cite the papers listed below.

name: GLaSS

version: 1

purpose: Computes spherical Bessel, tomographic and generalised lensing spectra.

attribution: Peter Taylor, Mullard Space Science Laboratory, University College London, 2018

cite:

• Preparing for the Cosmic Shear Data Flood: Optimal Data Extraction and Simulation Requirements for Stage IV Dark Energy Experiments: Generalised Shear Spectra are introduced.
• Testing the Cosmic Shear Spatially-Flat Universe Approximation with GLaSS: GLaSS, is introduced.

python dependencies

• numpy (for fast computation build against a linear algebra package like BLAS or Apple Acccelerate)
• os
• ctypesGsl
• math
• itertools

Running GLaSS

GLaSS is called by Cosmosis. Run-mode options are specified in a Cosmosis ini file. GLaSS can either be run like any other Cosmosis module or interactively in Python. See the jupyter notebooks to see how to run interactively.

Program Structure

GLaSS is run internally in Cosmosis. Cosmosis first calls setup(options) in GLaSS.py. This reads in and returns all the run-mode options that are specified in the Cosmosis ini file. Bessel function data is also computed inside this function as needed.setup(options) is only run once, each time Cosmosis is called. Then exec(block, config) is called. This function reads in the power spectrum data either from the Cosmosis pipeline or an external source. It then computes the lensing power spectra and returns this to the Cosmosis data block. The calculation is performed by the main function in lensing_calculation.py. All the functions that are actually used internally to perform the calculation of the lensing spectra are defined in lensing_calculation.py.

Run-mode Options

To see which run-mode options to use have a look at the ini files and jupyter lab notebook provided with GLaSS. It is also worth looking at the .py files called in the jupyter notebook. A complete list of run-mode options can be found by having a look at the code comments in the setup(options) function in GLaSS.py.

Output

_GLaSS returns the l samples, z samples, r(z) samples and k samples that were taken. Note that k is reutrned in units of Mpc ^ -1, not h Mpc ^ -1, which is the conevention. The shot noise and the lensing spectra are returned in a 2D array with dimensions: (resolution, resolution * number_of_l_modes) for spherical-bessel and arbitrary weighted lensing and (number_of_tomographic_bins, number_of_tomographic_bins * number_of_l_modes) for tomographic lensing spectra. The jupyter notebook shows how to exctract the relevant data.