You need any two points to get a striaght line. So I am selecting two random points to plot a line here.
% Random points to plot a line
P0 = rand(1,2) ;
P1 = rand(1,2) ;
x = [P0(1,1) P1(1,1)] ; % x coordinates
y = [P0(1,2) P1(1,2)] ; % y coordinates
% distance
d = sqrt(sum((P0-P1).^2)) ;
% divide into fpur equal parts
xi = linspace(P0(1),P1(1),4) ;
yi = interp1(x,y,xi) ;
% Mid point
M = (P0+P1)/2 ;
% plot
plot(x,y,'b')
hold on
plot(xi,yi,'-*r')
