185 lines
7.6 KiB
Markdown
185 lines
7.6 KiB
Markdown
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| **master** | **dev** |
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| ------------- | ------------- |
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| [](https://travis-ci.org/nlesc-dirac/sagecal) | [](https://travis-ci.org/nlesc-dirac/sagecal) |
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# SAGECAL
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## Features
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- Levenberg-Marquardt, LBFGS, Riemannian Trust Region, Nesterov's accelerated gradient descent algorithms
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- GPU acceleration using CUDA
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- Fast and accurate interferometric calibration
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- Gaussian and Student's t noise models
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- Shapelet source models
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- CASA MS data format supported
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- Distributed calibration using MPI - consensus optimization with data multiplexing
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- Tools to build sky models and restore sky models to images
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- Adaptive update of ADMM penalty (Barzilai-Borwein a.k.a. Spectral method)
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Read INSTALL for installation. This file gives a brief guide to use SAGECal.
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Warning: this file may be obsolete. use sagecal -h to see up-to-date options.
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## Step by Step Introduction:
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### 1) Input Data
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Input to sagecal must be in CASA MS format, make sure to create a column in the MS to write output data as well. The data can be in raw or averaged form, also initial calibration using other software can be also applied.
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### 2) Sky Model:
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#### 2a) Make an image of your MS (using ExCon/casapy).
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Use Duchamp to create a mask for the image. Use buildsky to create a sky model. (see the README file on top level directory). Also create a proper cluster file.
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Special options to buildsky: -o 1 (NOTE: not -o 2)
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Alternatively, create these files by hand according to the following formats.
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#### 2b) Cluster file format:
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cluster_id chunk_size source1 source2 ...
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e.g.
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```
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0 1 P0C1 P0C2
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2 3 P11C2 P11C1 P13C1
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```
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Note: putting -ve values for cluster_id will not subtract them from data.
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chunk_size: find hybrid solutions during one solve run. Eg. if -t 120 is used
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to select 120 timeslots, cluster 0 will find a solution using the full 120 timeslots while cluster 2 will solve for every 120/3=40 timeslots.
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#### 2c) Sky model format:
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```
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#name h m s d m s I Q U V spectral_index RM extent_X(rad) extent_Y(rad) pos_angle(rad) freq0
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```
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or
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```
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#name h m s d m s I Q U V spectral_index1 spectral_index2 spectral_index3 RM extent_X(rad) extent_Y(rad) pos_angle(rad) freq0
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```
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e.g.:
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```
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P1C1 0 12 42.996 85 43 21.514 0.030498 0 0 0 -5.713060 0 0 0 0 115039062.0
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P5C1 1 18 5.864 85 58 39.755 0.041839 0 0 0 -6.672879 0 0 0 0 115039062.0
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#A Gaussian mjor,minor 0.1375,0.0917 deg diameter -> radius(rad), PA 43.4772 deg (-> rad)
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#Position Angle: "West from North (counter-clockwise)" (0 deg = North, 90 deg = West).
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#Note: PyBDSM and BBS use "North from East (counter-clockwise)" (0 deg = East, 90 deg = North).
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G0 5 34 31.75 22 00 52.86 100 0 0 0 0.00 0 0.0012 0.0008 -2.329615801 130.0e6
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#A Disk radius=0.041 deg
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D01 23 23 25.67 58 48 58 80 0 0 0 0 0 0.000715 0.000715 0 130e6
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#A Ring radius=0.031 deg
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R01 23 23 25.416 58 48 57 70 0 0 0 0 0 0.00052 0.00052 0 130e6
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#A shapelet ('S3C61MD.fits.modes' file must be in the current directory)
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S3C61MD 2 22 49.796414 86 18 55.913266 0.135 0 0 0 -6.6 0 1 1 0.0 115000000.0
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```
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Note: Comments starting with a '#' are allowed for both sky model and cluster files.
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Note: 3rd order spectral indices are also supported, use -F 1 option in sagecal.
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Note: Spectral indices use natural logarithm, ```exp(ln(I0) + p1 * ln(f/f0) + p2 * ln(f/f0)^2 + ..)``` so if you have a model with common logarithms like ```10^(log(J0) + q1*log(f/f0) + q2*log(f/f0)^2 + ..)``` then, conversion is
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```
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ln(I0)+p1*ln(f/f0)+p2*ln(f/f0)^2+... = ln(10)*(log(J0)+q1*log(f/f0)+q2*log(f/f0))^2)+...)
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=ln(10)*(ln(J0)/ln(10)+q1*ln(f/f0)/ln(10)+q2*ln(f/f0)^2/ln(10)^2+...)
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```
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so
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```
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I0=J0
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p1=q1
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p2=q2/ln(10)
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p3=q3/ln(10)^2
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...
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```
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### 3) Run sagecal
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Optionally: Make sure your machine has (1/2 working NVIDIA GPU cards or Intel Xeon Phi MICs) to use sagecal.
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Recommended usage: (with GPUs)
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```
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sagecal -d my_data.MS -s my_skymodel -c my_clustering -n no.of.threads -t 60 -p my_solutions -e 3 -g 2 -l 10 -m 7 -w 1 -b 1
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```
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Use your solution interval (-t 60) so that its big enough to get a decent solution and not too big to make the parameters vary too much. (about 20 minutes per solution is reasonable).
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Note: It is also possible to calibrate more than one MS together. See section 4 below.
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Note: To fully use GPU acceleration use -E 1 option.
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Simulations:
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With -a 1, only a simulation of the sky model is done.
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With -a 1 and -p 'solutions_file', simulation is done with the sky model corrupted with solutions in 'solutions_file'.
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With -a 1 and -p 'solutions_file' and -z 'ignore_file', simulation is done with the solutions in the 'solutions_file', but ignoring the cluster ids in the 'ignore_file'.
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Eg. If you need to ignore cluster ids '-1', '10', '999', create a text file :
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```
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-1
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10
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999
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```
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and use it as the 'ignore_file'.
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### 4) Distributed calibration
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Use mpirun to run sagecal-mpi, example:
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```
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mpirun -np 11 -hostfile ./machines --map-by node --cpus-per-proc 8
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--mca yield_when_idle 1 -mca orte_tmpdir_base /scratch/users/sarod
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/full/path/to/sagecal-mpi -f 'MS*pattern' -A 30 -P 2 -r 5
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-s sky.txt -c cluster.txt -n 16 -t 1 -e 3 -g 2 -l 10 -m 7 -x 10 -F 1 -j 5
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```
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Specific options :
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```-np 11``` : 11 processes : starts 10 slaves + 1 master
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```./machines``` : will list the host names of the 11 (or fewer) nodes used ( 1st name is the master ) : normally the node where you invoke mpirun
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```-f 'MS*pattern'``` : Search MS names that match this pattern and calibrate all of them together. The total number of MS being calibrated can be higher than the actual number of slaves (multiplexing).
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```-A 30``` : 30 ADMM iterations.
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```-P 2``` : polynomial in frequency has 2 terms.
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```-Q``` : can change the type of polynomial used (```-Q 2``` gives Bernstein polynomials).
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```-r 5``` : regularization factor is 5.0.
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```-G textfile```: each cluster can have a different regularization factor, instead of using ```-r``` option when the regularization is the same for all clusters.
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MPI specific options:
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```/scratch/users/sarod``` : this is where MPI stores temp files (default is probably ```/tmp```).
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```--mca*```: various options to tune the networking and scheduling.
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Note: the number of slaves (-np option) can be lower than the number of MS calibrated. The program will divide the workload among the number of available slaves.
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The rest of the options are similar to sagecal.
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### 5) Solution format
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All SAGECal solutions are stored as text files. Lines starting with '#' are comments.
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The first non-comment line includes some general information, i.e.
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freq(MHz) bandwidth(MHz) time_interval(min) stations clusters effective_clusters
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The remaining lines contain solutions for each cluster as a single column, the first column is just a counter.
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Let's say there are K effective clusters and N directions. Then there will be K+1 columns, the first column will start from 0 and increase to 8N-1,
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which can be used to count the row number. It will keep repeating this, for each time interval.
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The rows 0 to 7 belong to the solutions for the 1st station. The rows 8 to 15 for the 2nd station and so on.
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Each 8 rows of any given column represent the 8 values of a 2x2 Jones matrix. Lets say these are ```S0,S1,S2,S3,S4,S5,S6``` and ```S7```. Then the Jones matrix is ```[S0+j*S1, S4+j*S5; S2+j*S3, S6+j*S7]``` (the ';' denotes the 1st row of the 2x2 matrix).
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When a cluster has a chunk size > 1, there will be more than 1 solution per given time interval.
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So for this cluster, there will be more than 1 column in the solution file, the exact number of columns being equal to the chunk size.
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### Additional Info
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See [LOFAR Cookbook Chapter](https://support.astron.nl/LOFARImagingCookbook/sagecal.html).
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