Can't plot polyfit

Question

Ander Azpitarte 2020-10-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/619208-can-t-plot-polyfit

评论： Adam Danz 2020-10-19

REGRE_FG=polyfit(FGS(86:99),FGS(86:99))
figure
plot(REGRE_FG)

I have this code where

[FGEl(86:99),FGS(86:99)]
ans =
0011   80.3471
0011   81.5330
0012   82.7614
0012   83.9897
0012   85.1755
0012   86.3615
0014   92.1641
0015   97.8820
0016  103.5999
0018  109.3179
0019  115.0781
0021  120.7112
0022  126.3021
0024  131.8082

However, MATLAB says:

Not enough input arguments.
Error in polyfit (line 56)
V(:,n+1) = ones(length(x),1,class(x));

Does anyone know how to solve this? Also, does anyone know how to write the polyfit equation?

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Answer 1

Star Strider 2020-10-19

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https://ww2.mathworks.cn/matlabcentral/answers/619208-can-t-plot-polyfit#answer_518438

编辑：Star Strider 2020-10-19

在 MATLAB Online 中打开

The polyfit function also needs to know what degree of polynomial you want to fit:

p = polyfit(x,y,n)

where ‘n’ is the degree (1=linear, 2=quadratic, etc.).

Also, in order to plot it, you will need to evaluate it first with the polyval function.

EDIT — (19 Oct 2020 at 198:10)

Since your data are linearly related, the full code would go something like this —

REGRE_FG=polyfit(FGEl(86:99),FGS(86:99),1);
REGRE_FG_fit = polyval(REGRE_FG,FGEl(86:99));
figure
plot(FGEl(86:99),FGS(86:99), 'p')
hold on
plot(FGEl(86:99), REGRE_FG_fit, 'r')
hold off
grid
xlabel('FGEl')
ylabel('FGS')

.

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Adam Danz 2020-10-19

refline() is another way of plotting the regression line, too (example), although it doesn't have an option to plot the error estimates like polyval does.

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