Fitting multiple intervals

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Revision as of 21:00, 22 June 2009

Fitting Multiple Intervals using the OSPEX 'Fit Options' GUI

Introduction

This section covers using the OSPEX 'Fit Options' GUI to fit multiple intervals. This document assumes that the user has a working knowledge of the procedure outlined in OSPEX Documentation for fitting a single interval.

The 'Fit Options' GUI Looping Procedure

Once a single interval has been fit it may be of interest to the user to view how various parameters change with time. One way to do this is to fit a series of intervals individually, however this is a time consuming process. The 'Fit Options' GUI has a number of different ways to automatically fit a series of time intervals selected by the user. To start the process the 'Fit Options' GUI should appear as below:

Fit Options GUI after a single completed fit

In this case a single fit has been completed and we would like to fit subsequent intervals. There are a few choices we must make. The first is to select the intervals we would like to fit. We can do this by selecting the first interval in the series, then selecting the last interval while holding down the SHIFT key. All intervals between the two selected intervals will also be highlighted at this point.

Our second decision is the loop mode. The 'Loop Mode' Button is on the left around the midpoint of the GUI. The loop mode determines how we will attempt to fit each interval in our selected series. The options are as follows:

Loop Mode Options

• Automatic - Attempts to fit each interval from starting parameters with no other user input, when lowest reduced chi-squared is reached the loop moves on to the next interval in the series and continues the process
• Manual First + Automatic - The user adjusts the starting parameters and does the fit on the first interval as described in OSPEX Documentation, once this fit is accepted all other fits are done automatically with no further user input
• Manual All Intervals - The user fits each interval as described in OSPEX Documentation. Looping through the intervals will set the starting parameters for each interval, but the user can modify them and must accept each fit for the loop to continue

The next choice is the loop direction. The 'Loop Direction' button is immediately to the right of the 'Loop Mode' button. This allows us to choose whether we want to start with the latest time and go backwards or start with the earliest time and go forwards. Accordingly the two options available are:

Loop Direction Options

• Forward - Starts at the earliest time and loops through all selected intervals to the latest time
• Backwards - Starts at the latest time and loops through all selected intervals to the earliest time

Now we must select our 'Parameter Initialization Method'. The choices for this are right below the 'Loop Mode' and 'Loop Directions' buttons. The 'Parameter Initialization Method' allows us to select the way in which starting parameters for each interval in the loop will be selected. It is broken up so we can select the starting parameters for the first interval fit by one method, then use a different method for the each subsequent interval. Our choices are as follows:

First Interval

• Program Defaults - The first interval fit will use the program default values for all parameters. This includes the value of the parameter as well as whether it is free or fixed
• Current Values (Shown Above) - The values are taken from the 'Show Func' display above the 'Loop Mode' and 'Loop Direction' buttons, the parameters are fixed or free in the same way they are in the Current Function displayed in 'Show Func'
• Final Fit Parameters from Interval: - Uses the final fit parameters from a chosen interval as the starting parameters for the first interval in the loop, the parameters are fixed or free as they are in the chosen interval
• Starting Fit Parameters from Interval: - Uses the starting parameters from a chosen interval as the starting parameters for the first interval in the loop, the parameters are fixed or free as they are in the chosen interval

Subsequent Intervals

• Program Defaults - All intervals after the first interval will use default values of the parameters as well as the default free or fixed values
• Fitted Parameters from most recently fit interval - All intervals after the first interval fit will use the final values of the last interval fit as their starting parameters including the free or fixed values
• Starting Parameters from most recently fit interval - All intervals after the first interval will use the starting parameters from the last interval fit as their starting parameters including the free or fixed values
• Fitted parameters from previous iteration on each interval - All intervals will use the value of the final fitted parameters from the last time that interval was fit. If no fit was was previously done on an interval, the current values from 'Show Func' will be used. Note that if this option is selected it is applied to the first interval as well, therefore you will not be allowed to choose a separate method for the first interval. All intervals will use their previous values for free and fixed unless they were never fit, in this case they will use the free or fixed values from the current interval.