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ccdpot - potential of an infinitesimally thin disk
**ccdpot** [parameter=value]
Computes the potential in the plane of an infinitesimally thin
disk. The method here is VERY slow, since it evaluates the integral exactly
given as Eq. 2-3 in e.g. *Galactic Dynamics* by Binney and Tremaine (1987). The
integral is replaced by a sum over the pixel values of the input image
of

Sigma(p)
Pot(P) = -Gravc * SUM ---------- dx dy
| p - P |

P, and p are vector positions, Sigma(p)
is the surface density at position
p. dx and dy are pixel sizes and the distance |p-P| is measured in pixels.

A faster way is to use FFT’s, as described by Hockney & Eastwood (1978),
and implemented in MIRIAD’s potfft program.

The following parameters
are recognized in any order if the keyword is also given:
**in=**
- Input image
file, in
*image(5NEMO)*
format. No default.
**out=**
- Output image file. No default.
**gravc=**
- Gravitional constant. Normally taken as 1, but this allows you to
more easily convert to your own units already. See also
*units(5NEMO)*
. Default:
1

potential(GIPSY), potfft(MIRIAD), image(5NEMO)
Since for
each of the N^2 pixels, all other N^2 pixels will be interrogated, this algorithm
is O(N^4). In practice you will find it to be more like O(N^5). The code precomputes
a kernel, which is simplified if we can assume the pixel size in X and
Y are the same. If not, the program will currently probably compute it terribly
wrong.
Peter Teuben (loosely based on Roelof Bottema’s POTENTIAL code)

26-Jul-02` ` ` ` V0.1 Created to check potfft PJT
22-oct-02` ` ` ` V0.2 correct kernel at (0,0)` ` ` ` PJT
28-feb-03` ` ` ` V0.3 added gravc=` ` ` ` PJT

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