polyaprox.m

First order linear regression that automatically provides error calculations and graphic visualizati

% Fit data to polynomial equation of first
% order or second order
%
%usage: val=polyaprox(xdata,ydata,degree)
% degree could take only values 1 or 2
% output the vector val
%       val=[m delta_m b delta_b r_square  ]
%

function val=polyaprox(x,y,graph,out)

	format long

	n=(length(x));

    p=polyfit(x,y,1);
    x1=linspace(min(x)- min(x)*0.005,max(x)+ max(x)*0.005,1000);
    y1=polyval(p,x1);
    m=p(1);
    b=p(2);
    
    r=(n*sum(x.*y)-sum(x)*sum(y))/(sqrt(n*sum(x.^2)-(sum(x))^2)*sqrt(n*sum(y.^2)-(sum(y))^2));
    dm=abs(m)*sqrt(((1/r^2)-1)/(n-2));
    db=dm*sqrt(sum(x.^2)/n);
    
    val=[m,dm,b,db,r^2];
    if out==1
        fprintf('\n m