x=[-1 0 2 3] 

format compact 

y=[0 -1 2 1] 

plot(x,y,'x') 

plot(x,y) 

plot(x,y,'*') 

A=[x;ones(1,4)]' 

c=A'*y' 

B=A'*A 

B\c 

d=B\c 

x0=linspace(-2,4,100); 

f1=d(1)*x0+d(2); 

plot(x,y,'*',x0,f1) 

polyfit(x,y,1) 

polyfit(x,y,2) 

polyfit(x,y,3) 

p=polyfit(x,y,3) 

p3=polyval(x0,p) 

p3=polyval(p,x0); 

plot(x,y,'*',x0,p3) 

polyfit(x,y,5) 

polyfit(x,y,4) 

a=0.25/35.6875 

b=(2-13.5*a)/4 

f2=a*2.^x0+b; 

plot(x,y,'*',x0,f2) 

A=[2.^x;ones(1,4)]' 

B=A'*A 

c=A'*y' 

B\c 

f2=ans(1)*2.^x0+ans(2); 

plot(x,y,'*',x0,f2)