GNU Octave

Time for action – using polyfit

1. Assume that we have loaded the relevant data into Octave and stored the leaf lengths of tree A and B in variables yA and yB. The corresponding heights are stored in xA and xB.
2. To fit the linear model to the data in yA, we do the following:

   octave:15> [cA sA] = polyfit(xA, yA, 1);
   

3. We must check if the fit made any sense at all. First, we can plot the resulting linear fit together with the data:

   octave:16> plot(xA, yA, 'rs', xA, sA.yf, 'r');
   

   and is shown in the figure below with red squares and a red line.

4. The fit of y^B to the third order polynomial follows the same procedure:

   octave:17> [cB  sB] = polyfit(xB, yB, 3);
   
   octave:18> hold on; plot(xB, yB, 'bv', xB, sB.yf, 'b');
   

   The plot is shown in the figure below:

   Note