Dear Brian,
The abbreviation pp means that the polynomial that is defined, is a piecewise polynomial. In the structure you can find 'the order' (at your file it is four) that tells you the number of coefficients used for each polynomial. The 'pieces' tells you how many polylines are used in the plot. (in your data the order is 17). For each polynomial the breaks are used to define the start and end points of each polynomial. The break is therefore an array of 17+1 inputs.
If you now like to know where your polyline intersects the line y=x, you could use this code:
clc;clear all;close all;
test=load('test');
fnplt(test.test); grid on;hold on;
x=linspace(0,150,1000);y=x;
plot(x,y); hold on;
mycv = fnbrk(test.test,[1 200]);
cuts = fnval(mycv, mean(fnzeros(fncmb(fncmb(mycv,[0,200]),'-',fncmb(mycv,[200,0])))));
intersection = [cuts(1,1) cuts(2,1)];
plot(intersection(1),intersection(2),'go');
Good luck! Christiaan
