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potccd - Create an image with potentials or densities from a potential
**potccd** [parameter=value]
*potccd* stores the potential
values of a potential descriptor (see potential(5NEMO)
) on a regular grid
in standard *image(5NEMO)*
format. It is also possible to store the Poissonian
density, either 2D or 3D. For this numerical derivatives of the force field
are used, and hence a small difference step needs to be given.
The
following parameters are recognized in any order if the keyword is also
given:
**out=**
- Output file (image). No default.
**potname=**
- Name of the
*potential(5NEMO)*
.
No default
**potpars=**
- Parameters for the potential.
**potfile=**
- Any optional
data file associated with the potential.
**x=**
- X-coordinate(s) to test potential
at. This should be a regular array, e.g. 1:10:0.2. Default: 0.
**y=**
- Y-coordinate(s)
to test potential at. Default: 0.
**z=**
- Z-coordinate(s) to test potential at.
Default: 0.
**t=**
- Time to test potential at
**mode=pot|ax|ay|az|ar|at|den**
- Output
mode. Choices are potential, accelerations in X, Y or Z, and density (which
needs dr>0). Default:
**pot**.
**dr=**
- Difference step used to compute numerical force
derivates that are used to compute Poissonian densities.
**ndim=**
- Number of
dimensions used in Poissonian density computation. Should be 2 or 3.

With
**ndim=2** the Z-coordinate is not ignored, and hence may give meaningless results
if forces depend on Z.
First a somewhat obscure way in to create
a map of an arbitrary function using the **potname=rotcur** lookup table. It
will use a spline interpolation, and if **mode=pot** is used, the "potential"
is actually the "rotation curve" itself, since in general one cannot easily
compute the potential from a rotation curve without knowing the full geometry.
Here is an example how to create a smooth radial profile of the function
"f(x)=1/sqrt(4+x)" on a grid from -10..10:

% nemoinp 0:10 | tabmath - - ’1/(sqrt(4+%1)’ > map0.tab
% potccd map0 rotcur 0 map0.tab x=-10:10:0.1 y=-10:10:0.1

If the functional form is know, *ccdmath(1NEMO)*
will perhaps do better,
if not a little more involved to type.
potlist(1NEMO)
, image(5NEMO)
,
potential(3NEMO)
, potential(5NEMO)
Peter Teuben

10-Jun-92` ` ` ` V1.0 Created ` ` ` ` PJT
30-mar-94` ` ` ` V1.1 added density options (dr=, ndim=)` ` ` ` PJT
12-sep-02` ` ` ` V1.2 added mode=` ` ` ` PJT

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