The analysis of weak lensing data requires to account for missing data such as masking out of bright stars. To date, the majority of lensing analyses uses the two point-statistics of the cosmic shear field. These can either be studied directly using the two-point correlation function, or in Fourier space, using the power spectrum. The two-point correlation function is unbiased by missing data but its direct calculation will soon become a burden with the exponential growth of astronomical data sets. The power spectrum is fast to estimate but a mask correction should be estimated. Others statistics can be used but these are strongly sensitive to missing data. 

The solution that is proposed by FASTLens is to properly fill-in the gaps with only NlogN operations, leading to a complete weak lensing mass map from which we can compute straight forwardly and with a very good accuracy any kind of statistics like power spectrum or bispectrum. The inpainting method relies strongly on the notion of sparsity and on the construction of sparse representations in large redundant dictionaries.


Simulated mass map with the mask pattern of CFHTLS data on D1 field (on the left), inpainted maps map (on the right).


FASTLens (Fast STatistics for weak Lensing) is a package written in C++ that includes:

- An inpainting code to derive complete weak lensing mass maps from incomplete shear maps

- A power spectrum estimator 

- A bispectrum estimator (for equilateral and isoscele configurations)

We propose also a new method to compute fastly and accurately the power spectrum and the bispectrum with a polar FFT algorithm.

User Manual

The user manual introduces the missing data problem in statistic estimation and presents the available routines. An accurate description of IDL routines is given.


The IDL FASTlens software requires IDL (version 6.0 or later) to be installed on your computer. 
The binaries C++ called by IDL routines are not available under all the systems therefore you cannot use the package on all platforms. The supported platforms are : PC-Linux and Mac OS X.

Inpainting routines (inpainting for weak lensing) 

Statistic routines (power spectrum and bispectrum estimators)


FASTLens (FAst STatistics for weak Lensing) : Fast method for weak lensing statistics and map making, S. Pires, J.-L. Starck, A. Amara, A. Refregier and J. Fadili, MNRAS,  395, 1265-1279, 2009

Acknowledging FASTLens

Please acknowledge use of the code in any resulting work, citing Pires, et al, 2009. We would be interested to collaborate with anyone requiring more advanced applications, and are always interested to hear about new applications. For questions and feedback or to be informed of the forthcoming versions, send an email to Sandrine Pires.

Contact information


Last modified on January 6th, 2015 by Sandrine Pires 
For questions and feedback or to be informed of the forthcoming versions, send an email to Sandrine Pires