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Hi,<br>
<br>
The numerical derivative for the Nth value y[N] is calculated as:<br>
der = y[N+1] - y[N-1] * 0.5 * deltaX<br>
where y is the potential deltaX is the difference between two
successive values in your input (e.g., 1 if you have a table that goes
from -180 to 180 with 361 values).<br>
<br>
I don't think you can print the number without changing the code, but
it's not difficult to calculate. You can plot your forces and -der and
see where they deviate. <br>
<br>
Ran.<br>
<br>
hong bingbing wrote:
<blockquote cite="mid877653.60202.qm@web15304.mail.cnb.yahoo.com"
type="cite">
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<div>Hi, Ran,</div>
<div><br>
</div>
<div>The potential f(x) and force -f'(x) in the table are calculated
by myself before constructing the table. The potential can be written
in an analytical form and the force is calculated as the analytical
negative derivative of the potential at point x. There should not be so
large deviation betw. the value I supplied and the value calculated by
GROMACS. Wait. Is there something wrong in my interpretation? What's
your method to get the force? Is there a way to see the numerical
derivative generated by GROMACS?</div>
<div><br>
</div>
<div>Thanks</div>
<div>CH</div>
</div>
</blockquote>
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