# PURIFY

## Description

PURIFY is a collection of routines written in C++ that implements different tools for radio interferometric imaging including file handling (for both visibilities and fits files), implementation of the measurement operator and set-up of the different optimization problems used for image deconvolution. The code calls the generic Sparse OPTimization (SOPT) package to solve the imaging optimization problems.

##Usage purify has two required arguments, --measurement_set and --name, the path of the measurement set and the prefix name of the output files.

purify --measurement_set path/to/measurements.ms --name output/path/name.

It is possible to add other options, such as limited the number of iterations to 100, and save output diagnostic images with each iteration. These

purify --measurement_set path/to/measurements.ms --name output/path/name --niters 100 --diagnostic

Arguments

Important Arguments

• --help will print basic help information, showing what arguments are possible (more than this list).
• --measurement_set is the path to the CASA measurement set folder. (required argument)
• --name is the prefix name used to save the output model, residual, and dirty map. (required argument)
• --diagnostic will record variables and output images with each iteration. This is useful for testing or trial runs, but will take up some more computation in calculating and saving diagnostic updates. The update images and diagnostic file will be used as a checkpoint, in the case that purify locates the images from a previous run.
• --l2_bound this value can be used to scale the error on the model matching the measurements. Default value is 1.4.
• --power_iterations number of iterations needed to normalize the measurement operator. This is needed to ensure that the measurement operator reconstruct a model to the correct flux scale. Default value is 100.
• --noadapt will turn off the adapting step size.
• --size the height and width of the output image in pixels (only powers of 2 supported at present).
• --cellsize is the width and height of a pixel in arcseconds. If not specified, this is determined from the Nyquist limit.
• --niters max number of iterations. Default is max unsigned integer.
• --relative_variation the relative difference of the model between iterations needed for convergence.
• --residual_convergence the upper bound on the residual norm needed for convergence.

## Contributors

PURIFY was initially created by Rafael Carrillo, Jason McEwen and Yves Wiaux but major contributions have since been made by a number of others. The full list of contributors is as follows:

• Rafael E. Carrillo
• Jason D. McEwen
• Yves Wiaux
• Luke Pratley
• Mayeul d'Avezac

## Running the main purify executable

The main purify executable lives either in the build directory or in the in the bin subdirectory of the installation directory.

## Reference

When referencing this code, please cite our related papers:

1. R. E. Carrillo, J. D. McEwen and Y. Wiaux. "PURIFY: a new approach to radio-interferometric imaging". Mon. Not. Roy. Astron. Soc., 439(4):3591-3604, 2014, arXiv:1307.4370
2. A. Onose, R. E. Carrillo, A. Repetti, J. D. McEwen, J.-P. Thiran, J.-C. Pesquet, and Y. Wiaux. "Scalable splitting algorithms for big-data interferometric imaging in the SKA era". Mon. Not. Roy. Astron. Soc., 462(4):4314-4335, 2016, arXiv:1601.04026
3. L. Pratley, J. D. McEwen, M. d'Avezac, R. E. Carrillo, A. Onose, Y. Wiaux. "Robust sparse image reconstruction of radio interferometric observations with PURIFY". Mon. Not. Roy. Astron. Soc., submitted, 2016

## Installation

### C++ pre-requisites and dependencies

• CMake: a free software that allows cross-platform compilation
• fftw3: Fastest Fourier Transform in the West
• tiff: Tag Image File Format library
• OpenMP: Optional. Speeds up some of the operations.
• casacore: Optional. Needed to interface with measurement sets. The main purify program requires this library (and its dependencies)
• UCL/GreatCMakeCookOff: Collection of cmake recipes. Downloaded automatically if absent.
• basp-group/sopt: Sparse Optimization Compressed Sensing library. Downloaded automatically if absent.
• Eigen 3: Modern C++ linear algebra. Downloaded automatically if absent.
• spdlog: Optional. Logging library. Downloaded automatically if absent.
• cfitsio: library of C and Fortran subroutines for reading and writing data files in FITS (Flexible Image Transport System) data format. Downloaded automatically if absent. Needed by CCFits.
• CCFits: c++ wrappers for cfitsio. Downloaded automatically if absent.
• philsquared/Catch: Optional - only for testing. A C++ unit-testing framework. Downloaded automatically if absent.
• google/benchmark: Optional - only for benchmarks. A C++ micro-benchmarking framework. Downloaded automatically if absent.

### Installing Purify

Once the dependencies are present, the program can be built with:

cd /path/to/code
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make

To test everything went all right:

cd /path/to/code/build
ctest .

To install in directory /X, with libraries going to X/lib, python modules to X/lib/pythonA.B/site-packages/sopt, etc, do:

cd /path/to/code/build
cmake -DCMAKE_INSTALL_PREFIX=/X ..
make install

### CMake Tips

It is possible to tell CMake exactly which libraries to compile and link against. The general idea is to add -DVARIABLE=something to the command-line arguments of CMake. CMake can be called any number of times: previous settings will not be overwritten unless specifically requested. Some of the more common options are the following:

• CMAKE_PREFIX_PATH: CMake will look in "CMAKE_PREFIX_PATH/lib" for libraries, "CMAKE_PREFIX_PATH/include" for headers, etc.
• PYTHON_EXECUTABLE, PYTHON_LIBRARIES, PYTHON_INCLUDE_DIRS
• FFTW3_LIBRARIES, FFTW3_INCLUDE_DIR
• BLAS_INCLUDE_DIRS, BLAS_LIBRARIES

All these variables and more can be found and modified in the CMakeCache.txt file in the build directory.

## SUPPORT

If you have any questions or comments, feel free to contact Rafael Carrillo or Jason McEwen, or add an issue in the issue tracker.

## NOTES

The code is given for educational purpose. The code is in beta and still under development.

## LICENSE

PURIFY Copyright (C) 2013 Rafael Carrillo, Jason McEwen, Yves Wiaux

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details (LICENSE.txt).

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.