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sfskewness

Section: User Commands (1)
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NAME

sfskewness - Computes an index of skewness of spherical functions.

 

SYNOPSIS

sfskewness -inputmodel <sh|rbf|maxent> [options]

 

DESCRIPTION

Computes the skewness of any input spherical function. The skewness of a function f is
the cube root of int(f(x) - F)^3/int(f^3(x)) where F = int(f(x)) and the integrals are all over the unit sphere. The program approximates the integrals by summing over a set of around 8000 points evenly distributed on the sphere. To decrease computation time, the size of the point set can be reduced using the -pointset option.

 

EXAMPLES

Here are some examples using synthetic data.

Create a synthetic data set:

datasynth -testfunc 3 -snr 16 -voxels 4 -schemefile test/bmx7.scheme > T3_BMX7.Bfloat

Fit the spherical harmonics with maximum order 2 and compute the skewness:

shfit -order 2 -schemefile test/bmx7.scheme < T3_BMX7.Bfloat | sfskewness -inputmodel sh -order 2 | double2txt

 -2.014889E-01
 -2.120732E-01
 -1.961482E-01
 -2.428282E-01

Try with maximum order 4: shfit -order 4 -schemefile test/bmx7.scheme < T3_BMX7.Bfloat | sfskewness -inputmodel sh -order 4 | double2txt 7.941038E-02 -1.698385E-01 -1.204264E-01 1.178613E-01

Repeat using PASMRI: mesd -filter PAS 1.4 -schemefile test/bmx7.scheme < T3_BMX7.Bfloat | sfskewness -inputmodel maxent -filter PAS 1.4 -mepointset 54 | double2txt 9.906369E-01 9.908336E-01 9.408537E-01 9.956099E-01

 

OPTIONS

-inputmodel <sh|rbf|maxent|dt>

Tells the program what type of functions are input. Currently supported options are:

sh - Spherical harmonic series. (Must specify -order.)

maxent - Maximum entropy representations output by mesd. (Must specify -filter and -mepointset.)

rbf - Sums of radial basis functions. (Must specify rbf parameters, eg -rbfsigma, and -rbfpointset.)

-pointset <|1|2|3|4|5|6|7>

Choose the point set used for the numerical integration. The point sets have sizes:

 0 - 1082
 1 - 1922
 2 - 4322
 3 - 8672
 4 - 15872
 5 - 32672
 6 - 72032
 7 - 78032

The default is point set 3.

 

SEE ALSO

fa(1), shfit(1), qballmx(1), mesd(1), sfanis(1), sfkurtosis(1)

 

BUGS

 

AUTHOR

Danny Alexander <camino@cs.ucl.ac.uk>

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Index

NAME

SYNOPSIS

DESCRIPTION

EXAMPLES

OPTIONS

SEE ALSO

BUGS

AUTHOR

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Time: 02:07:11 GMT, December 04, 2017