function [x,y,ytrue]=genData(n,sigma)
% [x,y] = genData(n,sigma)
%
% generate n points between -1 and 1, compute true value of f(x) and 
% add Gaussian noise with variance sigma^2
%
% [x,y,ytrue] = genData(...) also returns the "true" values of y (without
% the additive noise).

x=unifrnd(-1,1,1,n);
ytrue=sin(x);

noise = randn(1,n)*sigma;
y=ytrue+noise;