Adjusting Individual Curve Fit Band Limits, Invariance, and Locking
Band limits, invariance, and estimate locking are all set in the Fit
Parameters dialog by clicking All in the Select Bands dialog. The dialog reflects the
values of the currently selected band. Note that you can select bands from the
list box without closing the dialog. Use What's This help for information on the individual fields.
Adjusting Individual Limits
Sometimes, it is undesirable to have symmetrical limits, i.e. limits that are
+/- the estimate plus a single value. You may also wish to constrain the
individual limits differently for each band. You can manually adjust the limits
for each parameter of each band from the Fit Parameters dialog.
Normally, the limits of an estimate will be the estimate +/- the limit delta
defined in the Curve Fit dialog for that parameter. For example, a position of
200eV +/- 1eV results in limits of 199eV and 201eV. You can adjust these
limits to override the defaults in the Fit Parameters dialog. Also, the limits
maintain the deltas from the estimates if the estimates are adjusted. Using the
previous example, suppose you set the upper limit to 200.5eV. The lower limit is
still the estimate, 1eV, but the upper limit is the estimate + 0.5eV. If you
now change the estimate to 202eV, the upper limit maintains a delta of 0.5eV,
resulting in a limit of 202.5eV.
The only time the limits reset is after a curve fit is performed.
Setting the Invariance
The invariance for each parameter is the number of iterations that parameter
is held fixed during a curve fit. This gives more weight to that parameter
estimate during a fit. For example, an invariance of 10 holds the estimate for a
given parameter for 10 iterations. If a curve fit lasts 12 iterations, that
parameter is adjusted on the last 2 iterations only.
Parameter Locking
Clicking the lock button for a parameter locks that parameter for all iterations of a curve fit. The estimate is fixed.
Performing a Curve Fit
Additional Curve Fitting Topics