Time for action - using polyfit

1. 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. 2. To fit the linear model to the data in yA, we do the following:

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

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.

1. 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

Notice that I have used the plotting style format'rs' and'bv'. Depending on your plotting backend, this may not be supported. You can change it to, for example,'ro' and'b+'

What just happened?

polyfit finds the polynomial coefficients...