Table of Contents
potrot - query a NEMO potential in the XY plane, and derive a rotation
potrot computed the
"rotation curve" (as defined by sqrt(radius*radial_force)) of a potential.
Single slit rotation curves can be defined (by using a single given angle
p=) as well as averaged along a set of position angles (e.g. p=0:90:2).
following parameters are recognized in any order if the keyword is also
an example of taking a "rotation curve" along the major, minor and force
average of a Pfenniger(1984) bar. The three tables are then cut into a simpler
form and plotted using tabplot. With the default pgplot interface for yapp
they are colored rsp. red, green and blue.
- Name of potential, no default.
- Parameters for potential
(1st one is pattern speed). See potential(5NEMO)
for some examples.
- Any optional data file associated with potential.
- Radii to sample. Notice
for most potentials r=0 results in NaN’s or divisions by zero and generally
bad output. [0:2:0.1]
- Angles to sample (in degrees). If exactly two
angles are given, and niter > 0, an iterative approach is used (similar
to the one in potq(1NEMO)
) and is generally more accurate. If One angle
is given, an exact "rotation curve" along that (position) angle is give,
else an average force is used to derive the "rotation curve". Default:
0. (meaning slit rotation curve along the X axis)
- Time to test potential
at, if relevant [0.0]
- Use this instead of any returned pattern speed.
- Format used to print numbers [%g] **not used yet**
number of iterations to find the forces from which the rotation curve is
derived. Only used if exactly two angles p are given. Careful: at each iteration
the sample step is halved, doubling the CPU requirements. 
- Relative accuracy that stops the iterations. [0.001]
potrot pfenniger84 r=0.1:10:0.1 p=0 > tab1
potrot pfenniger84 r=0.1:10:0.1 p=90 > tab2
potrot pfenniger84 r=0.1:10:0.1 p=0:90:2 > tab3
tabmath tab1,tab2,tab3 - %1,%3,%6,%9 all | tabplot - 1 2,3,4 line=1,1 color=2,3,4
Here’s a comparison between various methods for the same Pfenniger potential,
at a radius where the force along major and minor axis differs most:
potrot pfenniger84 r=4 p=0
4 -0.0403306 0.401649
potrot pfenniger84 r=4 p=90
4 -0.0277544 0.333193
potrot pfenniger84 r=4 p=0:90:10
4 -0.031413 0.354474
potrot pfenniger84 r=4 p=0:90:2
4 -0.0311816 0.353166
potrot pfenniger84 r=4 p=0,90
### Warning [potrot]: Testing an iterative procedure: niter=10 eps=0.001000
4 0 0.352989 8
potrot pfenniger84 r=4 p=0,90 eps=0.0001 niter=20
4 0 0.352822 12
07-Feb-05 V0.1 Created PJT
Table of Contents