Not all my code is not publically available yet. I'm in the prosses of making it more user-friendly. However, I'm more than happy to collaborate and pass on my code. If there is anything you see that you think will be useful please email me.


A python package to make maps of Dark Matter form the distortions of the shapes of images of galaxies. The package can produce maps directly on the celestial sphere with no need to make a flat sky approximation. The software package and results were presented in the paper Mapping dark matter on the celestial sphere with weak gravitational lensing.


To download the package visit massmappy

Spin Spherical Harmonic Transform: Python Interface

SSHT is a sophisticated start-of-the-art software package for analysing data on the sphere. I have written a comprehensive python interface. This will be available at

I have been heavily involved in the development of a new release of s2let. A software package for analysing spherical images using wavelets.

Map-making Algorithms

Map-making algorithms designed to remove temperature to polarisation leakage in a cosmic microwave background experiment. By exploiting the functional form of common systematic effects we can disentangle them from the true polarisation signal. The method to remove this leakage is dependant on the experimental set up. Here I have developed algorithms suitable for the following set ups:


A differencing experiment with a large range of crossing angles for each pixel.

A differencing experiment with a large range of crossing angles for each pixel, with a stepped half wave plate.

A differencing experiment with a small range of crossing angles for each pixel, with a stepped half wave plate.


The algorithms were shown to be effective on simulations in Wallis et al. 2015 arXive:1503.03285, one such simulation is shown on figure to the right.

Fast Satellite Scan Generation

A code that generates the piontings and paralactic angles for satellite scan strategy. As imputs it takes the parameters of the mission: length, sampling frequency and parameters to describe the scan. It can output the pointings to a file (a very big file!), be called in other code to use the pointings or output quanaties that allow one to calculate the mitigation of a systematic effect by the scan. This code is used in a paper that is currently in prep to design the scan strategy for COrE++. The figure to the right shows an example time intigration after one year of observations.

Assymetric Beam Convolution Code

This is a parrallelised pixel based convolution code. As input it takes a CMB temperature power spectrum, and a general beam shape. On output it generates the 3D result of the convolution of a CMB temperature sky realisation with the assymetric beam. It can run at high resolution (Nside=2048) and still perform well. The figure to the right shows an example beam that I have used this code to convolve with the CMB sky.

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christophergrwallis "at" gmail "dot" com


Mullard Space Science Laboratory
University College London
Surrey RH5 6NT

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