Chi-Squared Fit Window Help

The Chi-Squared Fit Window is where you find which models out of the ones you initially selected best fit your data. DIRT won't let you open this window unless you have already entered your data into the Data Input Window.

The Chi-squared Plot Panel

The upper (yellow & white) panel is the plot panel. It starts with the plots of the selected model Total Flux and your data. If you have input Flux per Beam data, then the model interpolated in frequency and beam size to match your data is also plotted. If you add new data (or change old data) in the Data Input Window, the Chi-Squared Fit Window will automatically update itself.

Fitting of Total Flux is very fast. Fitting of Flux per Beam takes a little bit longer since the models must be interpolated in both frequency and beam size (essentially interpolating the Flux(freq,beam) plot in the Details Window) to match the frequencies and beam sizes of your data.

Chi-Squared Fit Window Chi-Squared TalkBack Window
The main panel of the Chi-Squared Fit Window, showing Data and Best Fit model. Click to see full-size. The Talk-Back panel of the Chi-Squared Fit Window, showing parameters of the best-fit model. Click to see full-size.

As with the Details Window, you can zoom in on any portion of the plot area. To zoom in, press and hold any mouse button and drag the mouse downwards to draw a box. To zoom out, drag the mouse upward to make a box in a similar fashion. Clicking on the 'AutoScale' button rescales the plot so that all the data fits, i.e., it zooms out all the way.

The Talk-Back Window

The lower (blue & white) panel is the Talk-Back window. The fit results are displayed there, along with the calculated mass (Msun) of the best-fit model. The mass is given as

M =  { 4PI/(3-p)}  rho i   rip  {ro3-p   -   ri3-p }

where p is the power law exponent for the density structure of the envelope, ro and ri are the envelope outer and inner radii, respectively, and rho i is the density at the inner radius.

The Show Menu

Most of the Menus on the Chi-Squared Window are self-explanatory. The Show Menu is especially important and is used to decide what traces should be on the plot. The choices (Data, Selected Model, Best Fit, Chisq vs. Model #) are all toggles. The default is  Data  and  Selected Model   toggled on and the others off. Changing a toggle will cause the plot to update. If  Chisq vs. Model # is on, a small pop-up window containing all the chi-squared values will appear after a fit is done. The Y-axis is initially scaled to show a moderate range centered around the median chi-squared value. The plot is zoomable in the usual way. To pop-down this plot, simply de-select  Chisq vs. Model #.

Chi-Squared Show Menu
The Chi-Squared Show Menu, which gives you the choice of what traces to show.
Chi-Squared vs. Model Number
The Chi-Squared vs. Model # pop-up window.

HEY! "Window Capture" printing of this window does not work quite right. The plot gets cut off (at least with some OS's and printers).  I'll try to get this fixed soon--mwp.

Dirt Help Navigation
Main Display Details Plot Data Input Chi-Squared


Please direct comments, criticisms, corrections and contributions to Marc Pound
Page last modified: Tuesday, 10-Jun-2003 14:24:10 EDT.