potfit wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== Punishments for Analytic Potentials ======
----

For analytic potentials it may sometimes be necessary to use additional punishments to keep the potential in a predefined parameter space. If the initial contraints, given in the parameter file
can not achieve this, then there is a special function which is called before every force calculation. This function can be used to check for additional contraints on analytic potentials.

The function is called ''apot_punish'' and can be found in ''functions.c''.

<code c>
/****************************************************************
 *
 * punish analytic potential for bad habits
 *
 ****************************************************************/

real apot_punish(real *params, real *forces)
</code>

The parameters are

**real *params**\\
<html>&nbsp;&nbsp;&nbsp;</html>This is the array with the new parameters, access it with ''params[idx[i]]'', where $i<\text{ndim}$.

**real *forces**\\
<html>&nbsp;&nbsp;&nbsp;</html>This is the global forces array, store additional punishments to ''forces[punish_par_p+ i]'', where $i<\text{ndim}$

Here is an example, where a function is punished if two parameters are too close together:

<code c>
/* punish m=n for universal embedding function */
    if (strcmp(apot_table.names[i], "universal") == 0) {
      x = params[j+ 2] - params[j+ 1];
      if (fabs(x) < 1e-6) {
	forces[punish_pot_p+ i] = apot_punish_value / (x * x);
	tmpsum += apot_punish_value / (x * x);
      }
    }
</code>

The return value is used to make //potfit// aware of these extra punishments.