Table of Contents

A potential stored on a grid could be a good approach when the potential is expensive to compute, though in orbit calculations this could limit the exact conservation of the integrals of motion such as energy.

Irregular grids are not forbidden
(see **x=,y=,z=**) but the *image(5NEMO)*
WCS descriptor will then be invalid.

**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.
**omega=**- Use
this instead of any returned pattern speed. Default: not used, the first
parameter in
**potpars=**is used. **ndim=**- Number of dimensions used in Poissonian density computation. Should be 2 or 3.
**nder=1|2**- Normally the density (
**mode=den**) is derived by first derivatives of the forces, but for some potentials the force was never implemented (e.g.**potname=gauss**). In this case the 2nd derivative of the potential will be needed, hence**nder=2**. Default: 1

% nemoinp 0:10 | tabmath - - ’1/(sqrt(4+%1)’ > map0.tab % potccd map0 rotcur 0 map0.tab x=-10:10:0.1 y=-10:10:0.1If the functional form is know,

Here is an example of an orbit integration in the analytical plummer potential, and in two gridded versions of the potential.

% mkorbit o1 1 1 0 -0.5 0 0 potname=plummer etot: -0.452350 % orbint o1 - 10000 0.01 ndiag=10000 | orblist - | tail -1 Energy conservation: 2.05084e-11 10000 100 -1.11384 -0.266207 0 0.557843 -0.315574 0 % potccd ccd1 plummer x=-2:2:0.01 y=-2:2:0.01 % orbint o1 - 10000 0.01 ndiag=10000 potname=ccd potfile=ccd1 | orblist - | tail -1 Energy conservation: 0.0050378 10000 100 -1.3835 -0.156784 0 0.408364 -0.319573 0 % potccd ccd2 plummer x=-2:2:0.0025 y=-2:2:0.0025 % orbint o1 - 10000 0.01 ndiag=10000 potname=ccd potfile=ccd2 | orblist - | tail -1 Energy conservation: 0.00073957 10000 100 -1.18841 -0.23806 0 0.518358 -0.3183 0

10-Jun-92V1.0 CreatedPJT 30-mar-94V1.1 added density options (dr=, ndim=)PJT 12-sep-02V1.2 added mode=PJT 19-mar-2021V2.1 added nder=PJT