# How to use polyfit() function in Matlab?

First of all i am new to Matlab, and not sure whether to use polyfit or something else for my problem.

I plotted a graph with the following matlab code:

 t=transpose(linspace(-1,1,50))
y=1./(1+25*t.^2)
n=10
A=fliplr(vander(t))
A=A(:,1:n)
x=A\y
u=linspace(-1,1,1000)
g=x(n)*ones(1,1000)
for \$i=(n-1):-1:1
g=g.*u+x(i)  end
plot(u,g,'-',t,y,'o')


Now my question is: plot the figure with polynomial fit of polynomial degree 2.
How should i do this?
Thanks

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for the coefficients of the polyfit function how I can change the format of this coefficients to the long? Plz help me as soon. – user83693 Jun 24 '13 at 14:20

## 1 Answer

So you want to fit y as a function of t, right? Use

p = polyfit(t,y,2);

fit = polyval(p,t);

plot(u,g,'-',t,y,'o',t,fit)

The first line is the built-in polynomial fit function. The number 2 is the degree which you specify and it returns the coefficients of the polynomial in p. Note degree 2 means three coefficients. The second line then evaluates the polynomial using the coefficients in p. And then the third, plots them all together.

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thank you, since you are familiar with math lab, could you answer this question too? Thanks math.stackexchange.com/questions/228552/… – ASROMA Nov 4 '12 at 0:43