PFChrom v5 Documentation Contents            AIST Software Home            AIST Software Support

Peak Fit with Graphical Update

This is the graphical peak fitting display window. It is accessed from the various peak fitting options. This procedure can optionally update the graphs as the fits progress. The procedure displays numerical indices of the fit s fits are updated.

This operation displays a PFChrom Graph containing both a Y and a Y2 plot. The Y plot will contain the constituent peaks. The Y2 plot will contain the data and the sum curve for the fitted model.

The peak fits are governed by the current fit Preferences accessible from the peak fitting options. Some of these options, such as the Robust Minimization and Built-In Peak Fn Constraints can dramatically affect the fit results. Others such as Curvature Matrix option can significantly affect the time required for fitting large data sets when many peaks are being fitted.

If a fit consistently indicates that it is wrestling with one or more constraints, it may mean that the constraints need to be opened somewhat, or perhaps cautiously disabled.

When a graphical fit is initiated, a separate thread is used to launch the peak fitting for each data set being fitted. If an <irf> model is being fitted, separate threads will be created for each peak within each data set. Responsiveness to intervention actions, such as toggling the iteration updating, or stopping or aborting the fitting, should be good.

The dialog that is shown will depend on whether you have a 4K or HD monitor. For 4K monitors, the full display will be used to accommodate up to 25 simultaneously fitted data sets.

Fitting in Background

To have the peak fit performed in the background, simply minimize the fitting window. Since PFChrom uses this lower priority fitting threads by default in the Preferences, foreground performance should not suffer in any way. The graphical iteration updates do not occur when minimized.

Informational Elements

· Iter - Indicates the current iteration in fitting. These will reset in various algorithms and accumulate in various ways.

· Constraints - The number of constraint violations occurring on the current iteration will appear after the iteration count. When the iterations are listed as 12{3}, this means iteration 12, three constraint violations occurring on that iteration. This is an important indicator to watch. If most of a fit is spent escaping constraint violations, it may suggest the need for more open constraint percents or better initial placement. Constraints are set in the Fit Preferences and when user defined peaks are created.

· Merit - The ppm unaccounted variance in the fit. The goodness of fit criterion that governs minimization will be, for least-squares, the sum of squared residuals. For Robust Minimizations, it will be that robust procedure's merit function (a robust procedure is set in the Fit Preferences). These are not generally as useful as observing the ppm of unaccounted variance, 1e6*(1-r²)

· Fstat - The best F statistic thus far achieved in the fit. This will only be the F-statistic for the current iteration's parameters if such estimates are adopted.

· rē - The rē coefficient of determination thus far achieved. This will only be the rē for the current iteration's parameters if such estimates are adopted. An rē of 1.0 is a perfect fit; an rē of 0.0 is a complete lack of fit.

· Time - The total time thus far elapsed in fitting. This will include all fits underway.

· Evl - The total number of function evaluations occurring in the fit. A single function evaluation consists of the computation of a given peak or background function and all associated partial derivatives. If one of the sparse curvature matrix options is set in the Fit Preferences, this value may be less the data count x function count. This count does not include the various function evaluations necessary for updating the graph.

· Data - The total number of data points and the extent of fit. "500/2" would mean every other point of a 500 point table is being fitted. The size of the reduced data prefits is set in the Fit Preferences.

· Parms - The total number of parameters fitted. This represents the size of matrix inverted with each iteration. A fit consisting of 35 parameters requires the inversion of a 35x35 matrix with each iteration.

· Focus - When a cycle peaks strategy is underway, this will reflect the peak currently given the principal focus

Iteration Update

When checked, each peak fit is graphically updated following each iteration where the parameter estimates are adopted by the fitting algorithm. This option can be toggled on and off while a fit is underway.

When the iteration update is unchecked, the peaks are graphed only at the beginning and at the conclusion of the fit. Fitting is generally much faster with this Iteration Update off.

Graphical Zoom-In

You may zoom in the graph while a fit is underway. If some peak becomes suspect in the course of fitting, simply place the cursor at one corner of the desired zoom in region, press and hold the left mouse button while moving to the opposite corner of the desired region. You may zoom-in either plot.

To clear the zoom-in, simply right click the mouse in the graph area.

Stop Current

This button will stop the fitting at its current iteration. It can be used when the fit is changing extremely slowly. Some fits may find themselves within a very narrow valley in parameter space, and even though convergence is not signaled, very little is to be gained by continuing the fit. The Stop Current button is only visible while a single data set fit is underway.

Abort Fit

The Abort Fit button is available both during and at the conclusion of a fit. When the estimates of one or more parameters go widely astray, the fitted result may be useless. This is often very apparent graphically. Such problems may arise if all parameter constraints have been disabled. When a fit is aborted you are returned to the AutoFit operation as if no fit had occurred. When many fits are simultaneously in motion, this option may come and go as certain steps in the fitting procedures must proceed to completion and cannot be aborted.

Additional Adjust

The Adjust Fit is available at the conclusion of the fit. When using this graphical fit option, you may observe a peak which does not fit as you may have wished it to. This option offers the means to update the scan with the current results of the fit, enabling you to graphically adjust the offending peak, or perhaps to numerically adjust or lock a parameter, prior to reinitiating the fitting. The Review is still accessible from the AutoFit placement procedure should you choose to make no adjustments. You are also returned from the Review to the placement screen after saving a fit, so this option is not needed if you wish to first Review the fit before making revisions.

Review Fit

The Review Fit option is available at the conclusion of a fit. It is used when you wish to proceed directly to PFChrom's Review.