can't find line of best fit from simple code

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Em
Em on 20 Jan 2022
Commented: Image Analyst on 28 Jan 2022
I can't get a line of best fit to my data using the code from the matlab polyfit page. Does anyone know what might be going wrong?
power=[70,56,42,28];
depth90_09 =[2.9000, 3.0000, 4.4000, 1.7000];
Fit = polyfit(power,depth90_09,2);
plot(polyval(Fit,power))
hold on
scatter(power,depth90_09)
Cheers!

Accepted Answer

Star Strider
Star Strider on 20 Jan 2022
The first argument to plot must be the independent variable vector. When I added that, it works!
(I broke out the polyval call as a separate assignment, for clarity.)
power=[70,56,42,28];
depth90_09 =[2.9000, 3.0000, 4.4000, 1.7000];
Fit = polyfit(power,depth90_09,2);
Val = polyval(Fit, power);
figure
plot(power, Val)
hold on
scatter(power,depth90_09, 'filled')
.
  5 Comments
Image Analyst
Image Analyst on 28 Jan 2022
@Em your code throws an error. What is the value of
depth50mms_09
Are you sure you want a fit and not an interpolation? The quadratic fit looks reasonable to me.

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