Can't plot polyfit

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 =

    0.0011   80.3471
    0.0011   81.5330
    0.0012   82.7614
    0.0012   83.9897
    0.0012   85.1755
    0.0012   86.3615
    0.0014   92.1641
    0.0015   97.8820
    0.0016  103.5999
    0.0018  109.3179
    0.0019  115.0781
    0.0021  120.7112
    0.0022  126.3021
    0.0024  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?

Answer 1

[Star Strider]

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')

.

[Adam Danz]

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.