How can I find the coefficients of a polynomial equation for fit the curve in MATLAB?
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yahya rezvani
on 10 Aug 2020
Commented: hosein Javan
on 10 Aug 2020
hello. my polynomial equation is ( V)=c0+c1*T+c2*(t^2)-c3*P-c4*P*T i want use data for find c0 ,c1, ...c4 coefficients (i want fit data with this equation)
my p,v,t data is
100000 , 0.956 , 19.4
100000 , 0.9717 , 71.1
10000000 , 0.959 , 41.8
80000000, 0.9725 , 161 ...
thank you.
2 Comments
Image Analyst
on 10 Aug 2020
Hosein, can you move this down to the Answers section below, rather than up here in Comments, which is used to ask people for clarification of their question. You can even earn credit if it's down there.
Accepted Answer
hosein Javan
on 10 Aug 2020
if "p" and "t" are both independant variables then your problem is in the form of "y=f(x,z)" or "v=f(p,t)".
x=[
19.4
71.1
41.8
161
180
]; % t
y=[
100000
100000
10000000
80000000
100000000
]; % p
z=[
0.956
0.9717
0.959
0.9725
0.9999
]; % z
sf = fit([y, x],z,'poly21')
plot(sf,[y,x],z)
look at command window,
sf(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y
V(t,p) = c0 +c1*T - c3*P +c2*(t^2) - c4*T*P
by comparing you will understant that:
c0=p00
c1=p10
c3=-p01
c2=p20
c4=-p11;
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