sfit object. can't get coefficients.

2015 3 3
3 个回答
更新时间：2020 6 8
4 次查看（30 天）

0 个投票

Hello. There is my code:
>> c = fit( [X, Z], Y, ft, opts );
>> c
Linear interpolant:
c(x,y) = piecewise linear surface computed from p
where x is normalized by mean 0.5 and std 0.2745
and where y is normalized by mean 227.7 and std 80.16
Coefficients:
p = coefficient structure
>> class(c)
ans =
sfit
>> coeffvalues(c)
ans =
TriangleSurfaceInterpolant with properties:
Type: 'Linear'
>> c.p
ans =
TriangleSurfaceInterpolant with properties:
Type: 'Linear'
>> c(0.3, 201)
ans =
26349
Is it possible to get coefficient of
c() function?

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回答（3 个）

Greig
Greig 2015-3-3

1 个投票

As Sean de Wolski points out in the question that you linked to, a interpolated surface fit has multiple sets of linear fit coefficients, one for each point in the data.
If you want to have just a single set of coefficients for the entire surface fit you will need to use a polynomial fit. For example, if you want to use a 2nd order polynomial in both x and z, set the fittype to 'poly22'. The c.p00, c.p10, c.p01, c.p11, c.p20, c.p02 will contain all of your coefficients.
If this is not what you are looking for could you gives us some more details about what your are wanting.

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almaz ham
almaz ham 2015-3-3
Greig, thank you for answer. See in the picture. There ar three set of points: PWM, RPS and SOC. I get this picture using result of fit() function. Now i want to get relationship: RPS and SOC ---> PWM. I mean i need to compute PWM value for pair of given SOC and RPS. I need equation to implement it in C code . And this equation should be as easy as possible. But
fit()
function can't give me this equation. Is there any matlab function to fit set of 3 variable? "...use a polynomial fit..." Did you mean
polyfit()
function?
Greig
Greig 2015-3-4
编辑：Greig 2015-3-4
Judging by the pic, you want a linear fit in both x and y, so fit() will give you the answer. What you want is...
c = fit([SOC, RPS], PWM, 'poly11');
As before c.p00, c.p10, c.p01 are the coefficients.
This fits a linear function in both SOC and RPS, that is...
PWM = p00 + p10 * SOC + p01 * RPS
You may want to try
cftool
The interactive fitting tool, that will allow you to play around with the type of fit you use, and it displays the stat
maitehar
maitehar 2020-6-8
Hello, reading this because is in the direction of what I want.
What if I want those coeficients,from a linear fit, for each fitted interval?
This is just because, by a linear fit, it simplifies a lot some calculations and allows me to propose an easy analitycal solution in my study.
Any ideas?
maitehar
maitehar 2020-6-8
Ah, got it! I'lll leave it here just in case someone checks this later:
The structure with all coeficient values from a linear fit is called:
your_fit_name.p.coefs
cheers,

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