Content-type: text/html Manpage of potfft

# potfft

Section: User Commands (1)

## NAME

potfft - Calculates the potential and Green's function for a 2D mass distribution

## CATEGORIES

map manipulation

pjt

## DESCRIPTION

POTFFT is a MIRIAD task that calculates the gravitational potential corresponding to a two-dimensional mass distribution, which is given to it in the form of an image. The image should be a face on view of a galaxy. See DEPROJECT and REGRID for tasks helping with this.

The method used is a a fast-Fourier algorithm (see Numerical Recipes, chapters 12 and 17 and Hockney and Eastwood, p213 (1st ed.).

## PARAMETERS

in
The input image. It must be a two-dimensional image with the number of pixels along each axis a power of two. Some maps may have a redundant 3rd axis, one fix it to reset naxis to 2:
```   puthd in=\$in/naxis value=2
```
No default.
out
Optional output image. It has the same dimensions as the input, with the density replaced by the corresponding gravitional potential. No default if no green output is used.
green
Optional output map containing the Green's function G. Convolving G with a surface density image (using miriads routine CONVOL) will result in a proper potential image as produced by out= in this program. By default Green's image is not output.
eps
The softening parameter in pixel units. The default is 1.0. (0.0 cannot be used).
h
The vertical scaleheight in pixel units when a sech^2 disk is used. The default is 0, meaning an infinitesimally thin disk.
Inner and outer radii and step size in radius in which G(r) is computed and output to a log file.
gravc
Gravitational constant. Default: 1
distance
Distance to the object in Mpc. If the distance is used, the units of softening length and scale height now must be given in parsecs rather than pixels. The program output will remind the user how many pc one pixels will with this assumed distance (4.848*pixel[arcsec] pc, per Mpc distance). Default: not used.
log
Output log file. Default is terminal.

## Index

NAME
CATEGORIES
PERSON RESPONSIBLE
DESCRIPTION
PARAMETERS

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Time: 18:35:38 GMT, July 05, 2011