Struggling to add the polynomial line

I've managed to use ployfit(X,Y,1) to get the two readings but I'm unsure on how to add the line and caption to the actual plot.

Any help?

[David Goodmanson]

Hi emily,

I take it you want to add the fitting straight line to the plot. The output of polyfit is a two-component vector P. Then for an array variable x (which could be the same as X) the fitting line is just y = polyval(P,x). Then you can do, for example

plot(X,Y,x,y)  

Answer 1

[KSSV]

n = 10 ;
x = 1:n ;
y = rand(size(x)) ;

p = polyfit(x,y,1) ;
yi = polyval(p,x) ; 

figure
hold on
plot(x,y,'*r')
plot(x,yi,'b')
legend('Original Points','Fitted Line')

[emily bristow]

Thank you! How would I add the equation for the straight line onto the plot?

My polyfit answers were -0.0018 and 2.9640

[KSSV]

n = 10 ;
x = 1:n ;
y = rand(size(x)) ;

p = polyfit(x,y,1) ;
yi = polyval(p,x) ; 
str = ['y=',num2str(p(2)),'*x','+',num2str(p(1))] ; 
figure
hold on
plot(x,y,'*r')
plot(x,yi,'b')
title(str)
legend('Original Points','Fitted Line')

[David Goodmanson]

Hi emily,

in case you don't want the equation in the title, take a look at the 'text' command.

Also, I have to disagree with KSSV on one detail. I think

plot(x,y,'*r',x,yi,'b')

is a better way to do things, partly because you don't have to use 'hold on'. And if you use 'hold on' and don't use 'hold off' after the plot commands, it can lead to problems later.

[emily bristow]

Thankyou!!!