To perform a Statistical Analysis on a **model** the
**statistics** experiment can be employed. For each of the
**model** ports occurring in the **perturb** section, a Gaussian
distribution of the setting at this port is used in the statistical
analysis. Note that *SIESTA* does not explicitly treat physical
units, thus the standard deviation (*sigma*) needs to be
specified in the same unit which is implicitly assumed for the
corresponding input port. The number of desired **model** evaluations
is given in the **samples** entry. As a result, we obtain the
statistical variations of the quantities at the **model**'s output
ports selected by **responses** which are recorded in the
**log** file.

Example 4.1 illustrates how the **statistics**
experiment can be utilized to explore the statistical behavior of a
MOS device with respect to variations of the gate mask. This
experiment will take 1000 statistical samples and monitor the drain
current *id* of the device, and the threshold voltage
*vt*.

1999-05-27