Tutorial 1

The project Tutorial 1 can be very useful as a starting point to make different types of function fits. The main page is illustrated in fig. 7.

Figure 7: Fitting page

The page has three main regions: header, body, and footer (I will not spend time with the footer).

• The header presents on the right side the links that allow the user to change the fitting modes(Basic, the default, Advanced, and Expert), to Upload the contents of a previous fit that was saved locally in you computer, to return to the MyFits page, or to Logout. In addition the user can list the different fits available in the project area, Recover the chosen one, or Download it and save it in you personal computer. On the left side the user has the possibility to save the current fit and choose the project area name and the name of the current fit. The date and time will be added to the name of the fit so that you will be able to go back in history.

• The body has three main regions that actually correspond to the three steps necessary to perform a function fit to a set of experimental data: 1$^{\rm o}$Data, 2$^{\rm o}$ - Plot Parameters, and 3$^{\rm o}$- Function and Parameters.
  1. Data has two text boxes. The first has by default a few comment lines that start with ``#'' and a few lines with numbers arranged in three columns and correspond the values of the variables $x$, $y$, $\epsilon_y$, where $\epsilon_y$ is the error estimate of $y$. The second box has a few lines that start by ``#'' by default and correspond to examples of operations which you can perform with the data in the Data Box. I think it is self explainatory but you should try it and contact me if you have problems with it. Calculate does what it means applies the calculation rules to the data.

  2. Plot Parameters allows for the set the plot details and I think it is self explaintory. One suggest you to check the grace doc file on how to write subscripts, superscripts, etc..

  3. The Function and Parameters part is the most interesting one. NUsers will see it like in fig. 7. PUsers will see it like in fig. 8. The difference is the option to call the AuxCode Editor and the Additional C code box.

     Figure 8: Fitting page

     

     Depending on the Fitting mode the contents of this area might change. You might try to change to Advanced mode and Recover the fit Advanced-1.

     Once you defined the variables name, declare them, write your C code to calculate the value of the dependent variable you have to Compile the function. If you get back the string Compiled without errors everything is OK and you should see a table below where you will identify the fitting parameters that you defined in your function. There is a compilation log file where you can check what is wrong with your function. This table has buttons to fix or free each parameter, and three columns with boxes where: Value can receive the starting value in the numerical fit and will contain the output result of your fit, Min, and Max allow you to set the lower and upper limits in the parameters space where the fitting program will have to try to find the best fit. A last column Error will present you the error estimate of each fitted parameter.