Statistics Toolbox

An Interactive GUI for Nonlinear Fitting and Prediction

The function nlintool for nonlinear models is a direct analog of rstool for polynomial models. nlintool calls nlinfit and requires the same inputs.

The purpose of nlintool is larger than just fitting and prediction for nonlinear models. This GUI provides an environment for exploring the graph of a multidimensional nonlinear function.

Start by loading the data set reaction.mat and starting nlintool. The chemistry behind the data in reaction.mat deals with reaction kinetics as a function of the partial pressure of three chemical reactants: hydrogen, n-pentane, and isopentane.

• load reaction
  nlintool(reactants,rate,'hougen',beta,0.01,xn,yn)
  

You will see a "vector" of three plots. The dependent variable of all three plots is the reaction rate. The first plot has hydrogen as the independent variable. The second and third plots have n-pentane and isopentane respectively.

Each plot shows the fitted relationship of the reaction rate to the independent variable at a fixed value of the other two independent variables. The fixed value of each independent variable is in an editable text box below each axis. You can change the fixed value of any independent variable by either typing a new value in the box or by dragging any of the three vertical lines to a new position.

When you change the value of an independent variable, all the plots update to show the current picture at the new point in the space of the independent variables.

Note that while this example only uses three reactants, nlintool can accommodate an arbitrary number of independent variables. Interpretability may be limited by the size of your monitor for large numbers of inputs.

Example: Nonlinear Modeling

Regression and Classification Trees