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Testing Parallel Processing in CASA 5.3

Checking the output from tclean

CASA Parallelization Overview

Here I test the tclean task with CASA 5.3, comparing the output generated by using different numbers of cores. See the instructions here.

Following on from the previous tests we compare the average spectra. These are generated from a cube with 10% trimmed from the spectral axis, and a large circle, including most of the emission, extracted in the spatial plane.

Initial conclusions:
■ The statistics of the cleaned cubes continue to differ depending on the number of cores selected. The effect is marginal, but is more pronounced in some regions of the map.
■ Taking average spectra from a few pixels around a bright sources shows a max difference in a fitted peak of ~15% (between n=9 & n=3, towards the left hand peak in the plots below). Little to no difference towards a source in the right hand peak, and no difference at the brightest point in the map (peak integrated), or towards the top source (not included in the average spectra plots).
■ There may be a pattern in the emission recovered from the left hand peak. High average spectra : n=5,9,13, Low average spectra : n=3,7,11.

Average spectra inside circle (see plot on right)
n=9 - n=7 difference cube (contours: n=9 integrated)
n=9 / n=7


Full spectral cube

Spectrally and spatially trimmed integrated image

N(cores)=1
Pixel sum              : 200384
Pixel mean             : 0.000321857
Standard deviation     : 0.0752239
Skewness               : -5.10236
Kurtosis               : -3.04114
Minimum pixel value    : -127.512
   At pixel            : (1581, 1136, 86, 1)
Maximum pixel value    : 73.6167
   At pixel            : (43, 1425, 119, 1)
Pixel median           : -1.19904e-06
Total number of pixels : 622592000
Number of pixels used  : 622585773 (100.0%)
No. of pixels excluded : 6227 (0.0%)

Pixel sum              : 9.97593e+08
Pixel mean             : 243.553
Standard deviation     : 6197.4
Skewness               : 8.07061
Kurtosis               : -2.97319
Minimum pixel value    : -602863
   At pixel            : (1581, 1136)
Maximum pixel value    : 378257
   At pixel            : (1420, 1509)
Pixel median           : -0.109765
Total number of pixels : 4096000
Number of pixels used  : 4096000 (100.0%)
No. of pixels excluded : 0 (0.0%)

N(cores)=5
Pixel sum              : 274325
Pixel mean             : 0.000440623
Standard deviation     : 0.0752474
Skewness               : 7.90136
Kurtosis               : -3.07584
Minimum pixel value    : -75.0906
   At pixel            : (843, 2176, 59, 1)
Maximum pixel value    : 104.372
   At pixel            : (1576, 1141, 137, 1)
Pixel median           : -5.03141e-07
Total number of pixels : 622592000
Number of pixels used  : 622585810 (100.0%)
No. of pixels excluded : 6190 (0.0%)
Pixel sum              : 1.07687e+09
Pixel mean             : 1378.64
Standard deviation     : 10106.6
Skewness               : 2.90791
Kurtosis               : -3.35131
Minimum pixel value    : -29732.8
   At pixel            : (775, 1280)
Maximum pixel value    : 137202
   At pixel            : (888, 1221)
Pixel median           : 132.339
Total number of pixels : 4096000
Number of pixels used  : 781109 (19.1%)
No. of pixels excluded : 3314891 (80.9%)
N(cores)=7
Pixel sum              : 275571
Pixel mean             : 0.000442623
Standard deviation     : 0.0752186
Skewness               : 2.48467
Kurtosis               : -3.04699
Minimum pixel value    : -65.8146
   At pixel            : (803, 628, 22, 1)
Maximum pixel value    : 71.1451
   At pixel            : (47, 1749, 8, 1)
Pixel median           : -5.18267e-07
Total number of pixels : 622592000
Number of pixels used  : 622585899 (100.0%)
No. of pixels excluded : 6101 (0.0%)
Pixel sum              : 1.08106e+09
Pixel mean             : 1384.01
Standard deviation     : 10103.8
Skewness               : 2.95316
Kurtosis               : -3.17464
Minimum pixel value    : -28712.3
   At pixel            : (1075, 988)
Maximum pixel value    : 137438
   At pixel            : (888, 1221)
Pixel median           : 117.755
Total number of pixels : 4096000
Number of pixels used  : 781109 (19.1%)
No. of pixels excluded : 3314891 (80.9%)
N(cores)=9
Pixel sum              : 306768
Pixel mean             : 0.000492732
Standard deviation     : 0.0752929
Skewness               : 7.33751
Kurtosis               : -2.91486
Minimum pixel value    : -66.5957
   At pixel            : (87, 1170, 53, 1)
Maximum pixel value    : 86.3653
   At pixel            : (44, 1436, 51, 1)
Pixel median           : -2.41406e-07
Total number of pixels : 622592000
Number of pixels used  : 622585689 (100.0%)
No. of pixels excluded : 6311 (0.0%)
Pixel sum              : 1.22334e+09
Pixel mean             : 1566.16
Standard deviation     : 10145.5
Skewness               : 2.97839
Kurtosis               : -3.23465
Minimum pixel value    : -29447.3
   At pixel            : (1075, 988)
Maximum pixel value    : 138061
   At pixel            : (888, 1221)
Pixel median           : 244.476
Total number of pixels : 4096000
Number of pixels used  : 781109 (19.1%)
No. of pixels excluded : 3314891 (80.9%)

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