- description: sddsexpfit does exponential fits to a single column of an SDDS file as a
function of another column (the independent variable). The fitting function is
where x is the independent variable, C is the constant term, F is the factor, and R is the rate.

- examples: Fit an exponential decay to vacuum pressure versus time during a pumpdown:
sddsexpfit vacDecay.sdds -columns=Time,Pressure vacDecay.fit

Same, but give the program a hint and force it to get a better fit

sddsexpfit vacDecay.sdds -columns=Time,Pressure vacDecay.fit -clue=decays -tolerance=1e-12

- synopsis:
sddsexpfit [-pipe=[input][,output]] [inputFile] [outputFile] [-columns=xName,yName] [-tolerance=value] [-clue={grows | decays}] [-guess=constant,factor,rate] [-verbosity=integer] [-fullOutput]

- files: inputFile contains the columns of data to be fit. If inputFile contains multiple pages, each page of data is fit separately. outputFile has columns containing the independent variable data and the corresponding values of the fit. The name of the latter column is constructed by appending the string Fit to the name of the dependent variable. In addition, if -fullOutput is given, outputFile includes a column with the dependent values and the residual (dependent values minus fit values). The name of the residual column is constructed by appending the string Residual to the name of the dependent variable. outputFile contains four parameters: expfitConstant, expfitFactor, expfitRate, and expfitRmsResidual. The first three parameters are respectively C, F, and R from the above equation. The last is the rms residual of the fit.
- switches:
- -pipe=[input][,output] — The standard SDDS Toolkit pipe option.
- -columns=xName,yName — Specifies the names of the independent and dependent columns of data.
- -tolerance=value — Specifies how close sddsexpfit will attempt to come to the optimum fit, in terms of the mean squared residual. The default is 10-8.
- -clue={grows | decays} — Helps sddsexpfit decide whether the data is a decaying or growing exponential, i.e., whether R is negative or positive, respectively. If sddsexpfit is having trouble, this will often help.
- -guess=constant,factor,rate — Gives sddsexpfit a stating point for each of the three fit parameters.
- -fullOutput — Specifies that outputFile will contain the original dependent variable data and the fit residuals, in addition to the independent variable data and the fit values.
- -verbosity=integer — Specifies that informational printouts are desired during fitting. A larger integer produces more output.

- see also:
- author: M. Borland, ANL/APS.