Extrapolation of data points

Hi everyone.

I have calculated and plotted a set of x and y values. Let's say I have 20 points in my figure.

I want to use my first five point to extrapolate backwards to intercept the y-axis.

Can anyone help me with this?

Thank you :)

Answer 1

[Star Strider]

I am not certain exactly what you want.

See if this works for you:

x = sort(rand(1, 20));                                  % Create Data
y = sort(rand(1, 20));                                  % Create Data

x_5 = x(1:5);
y_5 = y(1:5);

b = [ones(size(x_5(:))), x_5(:)]\y_5(:);                % Estimate Parameters
y_int = b(1);                                           % Y-Intercept

y_xtrp = [ones(size([0; x_5(:)])), [0; x_5(:)]]*b;      % Create Line

figure(1)
plot(x, y, 'bp')
hold on
plot([0; x_5(:)]', y_xtrp', '--r')
hold off
grid