Subtracting polynomial from piecewise polynomial

Hello, I have a piecewise polynomial and I want to subtract from it. How would I go about doing this?

Thanks!

[Riccardo Scorretti]

Hi Nathan, could you post part of your code? You have a polynomial in which format? Coefficients only? Symbolic?

Answer 1

[Bruno Luong]

x=cumsum(rand(1,5));
x = x-mean(x);
% Test pp
y=rand(size(x));
pp=spline(x,y);

% Here is ppsubx2 a pp-form of pp-x^2
x0=pp.breaks(1:end-1)';
ppsubx2=pp;
ppsubx2.coefs = ppsubx2.coefs - [zeros(ppsubx2.pieces,ppsubx2.order-3), ones(size(x0)), 2*x0, x0.^2];

% Check
xi = linspace(min(x),max(x));
figure
plot(xi, ppval(pp,xi)-xi.^2, 'b', xi, ppval(ppsubx2,xi), 'r+');