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@teuben
teuben committed Dec 8, 2023
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Expand Up @@ -32,7 +32,7 @@ <h2><a name='sect2' href='#toc2'>Description</a></h2>
<h2><a name='sect3' href='#toc3'>Parameters</a></h2>
The following parameters are recognized in
order; they may be given in any order if the keyword is also given. Use
--help to confirm this man page is up to date.
<b>--help</b> to confirm this man page is up to date.
<dl>

<dt><b>in</b>=<i>in-file</i> </dt>
Expand All @@ -46,8 +46,7 @@ <h2><a name='sect3' href='#toc3'>Parameters</a></h2>
<dt><b>neib</b>=<i>value</i> </dt>
<dd>Number of neighbors used to determine
the local density. The default of 6 is the recommended value by Casertano
&amp; Hut (1985) [default: 6].
<p> </dd>
&amp; Hut (1985) [default: 6]. </dd>

<dt><b>rneib</b>=<i>value</i> </dt>
<dd>Initial radius to search the neighbors.
Expand Down Expand Up @@ -128,60 +127,65 @@ <h2><a name='sect4' href='#toc4'>Notes</a></h2>
<h2><a name='sect5' href='#toc5'>Examples</a></h2>
The following example takes
an N-body snapshot, sort the particles in the order of the distance from
the C.M., and calculate local density. <br>
<pre> snapcenter nbody.dat nbody.centered
snapsort nbody.centered nbody.sorted
hackdens nbody.sorted nbody.density
</pre>One can also weight the particles by its potential to some power. For this
we create a Plummer sphere, without centering, and compute the center in
two ways: <br>
<pre> mkplummer - 100 zerocm=f | snapsort - - rank=r &gt; p.dat
snapcenter p.dat . report=t
hackdens p.dat - | snapcenter - . weight=dens report=t
hackforce p.dat - | snapcenter - . weight="-phi*phi*phi" report=t
hackforce p.dat - | snapcenter - . weight="phi*phi*phi*phi" report=t

</pre>Note that in this case the Plummer sphere should have the correct mathematical
the C.M., and calculate local density.
<p> snapcenter nbody.dat nbody.centered<br>
snapsort nbody.centered nbody.sorted <br>
hackdens nbody.sorted nbody.density<br>

<p> One can also weight the particles by its potential to some power. For
this we create a Plummer sphere, without centering, and compute the center
in two ways:
<p> mkplummer - 100 zerocm=f | snapsort - - rank=r &gt; p.dat<br>
snapcenter p.dat . report=t<br>
hackdens p.dat - | snapcenter - . weight=dens report=t<br>
hackforce p.dat - | snapcenter - . weight="-phi*phi*phi" report=t<br>
hackforce p.dat - | snapcenter - . weight="phi*phi*phi*phi" report=t<br>
<br>
Note that in this case the Plummer sphere should have the correct mathematical
center, and not <i>centered</i>. This snippet of code is expanded in a script $NEMO/scripts/csh/centering.sh,
in which these different methods can also be applied to different models,
as expanded in the following table. <br>
<pre> nbody=100 models: Plummer King1 King3 King5 DeVauc
-------------------------------------------------------------
snapcenter on m: 0.102 0.029* 0.030* 0.033 0.299
snapcenter on dens: 0.060 0.039 0.036 0.030 0.030*
snapcenter on phi: 0.053
snapcenter on phi^2: 0.050*
snapcenter on phi^3: 0.052 0.032 0.030 0.026* 0.035
snapcenter on phi^4: 0.054 0.034 0.032 0.027 0.031
snapcenterp: 0.080
snapmnmx on min phi: 0.122
snapmnmx on m 50% phi: 0.058
snapmnmx on m 33% phi: 0.063 0.053
snapmnmx on m 25% phi: 0.067
rockstart on m: 0.082:
A (*) denotes the best method for that model.
</pre>Although for a Plummer sphere the best method is more than twice as good
than the worst method, this does not apply to other models. <p>
as expanded in the following table.
<p> nbody=100 models: Plummer
King1 King3 King5 DeVauc<br>
-------------------------------------------------------------<br>
snapcenter on m: 0.102 0.029* 0.030* 0.033 0.299<br>
snapcenter on dens: 0.060 0.039 0.036 0.030 0.030*<br>
snapcenter on phi: 0.053<br>
snapcenter on phi^2: 0.050*<br>
snapcenter on phi^3: 0.052 0.032 0.030 0.026* 0.035<br>
snapcenter on phi^4: 0.054 0.034 0.032 0.027 0.031<br>
snapcenterp: 0.080<br>
snapmnmx on min phi: 0.122<br>
snapmnmx on m 50% phi: 0.058<br>
snapmnmx on m 33% phi: 0.063 0.053<br>
snapmnmx on m 25% phi: 0.067<br>
rockstart on m: 0.082:<br>

<p> A (*) denotes the best method for that model.
<p>
<p> </pre>Although for a Plummer
sphere the best method is more than twice as good than the worst method,
this does not apply to other models. <p>
<a href='density.1falcON.html'><i>density(1falcON)</i></a>

is considerable faster, about twice with their K=32 default. <br>
<pre>mkplummer - 100000 |is considerable faster, about twice with their K=32 default.

snapscale - - mscale=10 |about twice with their K=32 default.
snapsort - - |about twice with their K=32 default.
density - - give=mxvr |about twice with their K=32 default.
snapshell - &rsquo;10**[-4:4:0.1]&rsquo; dens |about twice with their K=32 default.
tabmath - - &rsquo;log(%1),log(%4)&rsquo; all |
tabplot - 1 2 -4 4 -14 2 line=1,1 point=2,0.1
vs.
mkplummer - 100000 |line=1,1 point=2,0.1
snapscale - - mscale=10 |
snapsort - - |
hackdens - - |
snapshell - &rsquo;10**[-4:4:0.1]&rsquo; dens |
tabmath - - &rsquo;log(%1),log(%4)&rsquo; all |
tabplot - 1 2 -4 4 -14 2 line=1,1 point=2,0.1
</pre>
is considerable faster,
about twice with their K=32 default.
<p> mkplummer - 100000 |\ snapscale - -
mscale=10 |\<br>
snapsort - - |\<br>
density - - give=mxvr |\<br>
snapshell - &rsquo;10**[-4:4:0.1]&rsquo; dens |\<br>
tabmath - - &rsquo;log(%1),log(%4)&rsquo; all |\<br>
tabplot - 1 2 -4 4 -14 2 line=1,1 point=2,0.1<br>

<p> vs.
<p> mkplummer - 100000 |\ snapscale - - mscale=10 |\<br>
snapsort - - |\<br>
hackdens - - |\<br>
snapshell - &rsquo;10**[-4:4:0.1]&rsquo; dens |\<br>
tabmath - - &rsquo;log(%1),log(%4)&rsquo; all |\<br>
tabplot - 1 2 -4 4 -14 2 line=1,1 point=2,0.1<br>

<p>
<p>
<h2><a name='sect6' href='#toc6'>Bugs</a></h2>
The local density is calculated using (neib-1)th neighbor. Calculation
Expand Down Expand Up @@ -233,11 +237,11 @@ <h2><a name='sect11' href='#toc11'>History</a></h2>
6-jul-89<tt> </tt>&nbsp;<tt> </tt>&nbsp;doc updated?<tt> </tt>&nbsp;<tt> </tt>&nbsp;Jun
23-oct-90<tt> </tt>&nbsp;<tt> </tt>&nbsp;doc updated<tt> </tt>&nbsp;<tt> </tt>&nbsp;Peter
18-jul-92<tt> </tt>&nbsp;<tt> </tt>&nbsp;printf -&gt; dprintf to make it pipable<tt> </tt>&nbsp;<tt> </tt>&nbsp;Peter
24-may-02<tt> </tt>&nbsp;<tt> </tt>&nbsp;fixed running out of bits for large-N systems<tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
24-may-02<tt> </tt>&nbsp;<tt> </tt>&nbsp;fixed running out of bits for large-N <tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
11-aug-2022<tt> </tt>&nbsp;<tt> </tt>&nbsp;added example hackforce vs. hackdens<tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
21-sep-2023<tt> </tt>&nbsp;<tt> </tt>&nbsp;added direct=<tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
11-oct-2023<tt> </tt>&nbsp;<tt> </tt>&nbsp;V3.0 added norm=1 as a new default<tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
12-oct-2023<tt> </tt>&nbsp;<tt> </tt>&nbsp;V3.0 - proper mass scaling as well as nbody scaling<tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
12-oct-2023<tt> </tt>&nbsp;<tt> </tt>&nbsp;V3.0 proper mass/nbody scaling <tt> </tt>&nbsp;<tt> </tt>&nbsp;PJT
</pre><p>

<hr><p>
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