can't find line of best fit from simple code

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Em
Em 2022-1-20
评论： Image Analyst 2022-1-28
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!

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采纳的回答

Star Strider
Star Strider 2022-1-20
Ran in:
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')
.
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Em
Em 2022-1-28
编辑：Image Analyst 2022-1-28
Thank you for all your help Star Strider! For some reason my lines of best fit don't seem to be accurate for some of the data sets. Do you know why that might be?
Here is my code:
power=[70,56,42,28];
depth90_09 =[2.9000, 3.0000, 4.4000, 1.7000];
depth50_09 =[4.3,3.4,1.8,1.4];
depth50_08 =[3,2.3,1.2,1.5];
depth50_07 =[3.3,3.3,1.2,1.6];
depth50_06 =[4,2.6,2.5,0.5];
depth50_05 =[2.7,2.7,1.8,1];
depth50_04 =[3.5,2.3,1.1,0.7];
depth50_03 =[2.8,1.4,0.7,1];
depth50_02 =[0.6,1.1,0.7,0];
power_v = linspace(min(power), max(power), 150);
Fit = polyfit(power,depth90_09,2);
Valdepth90_09 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth90_09)
hold on
scatter(power,depth90_09, 'filled')
%%%%%%
Fit = polyfit(power,depth50mms_09,2);
Valdepth50mms_09 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_09)
hold on
scatter(power,depth50_09, 'filled')
%%
Fit = polyfit(power,depth50mms_08,2);
Valdepth50mms_08 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_08)
hold on
scatter(power,depth50_08, 'filled')
%%
Fit = polyfit(power,depth50mms_07,2);
Valdepth50mms_07 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_07)
hold on
scatter(power,depth50_07, 'filled')
%%
Fit = polyfit(power,depth50mms_06,2);
Valdepth50mms_06 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_06)
hold on
scatter(power,depth50_06, 'filled')
%%
Fit = polyfit(power,depth50mms_05,2);
Valdepth50mms_05 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_05)
hold on
scatter(power,depth50_05, 'filled')
%%
Fit = polyfit(power,depth50mms_04,2);
Valdepth50mms_04 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_04)
hold on
scatter(power,depth50_04, 'filled')
%%
Fit = polyfit(power,depth50mms_03,2);
Valdepth50mms_03 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_03)
hold on
scatter(power,depth50_03, 'filled')
%%
Fit = polyfit(power,depth50mms_02,2);
Valdepth50mms_02 = polyval(Fit, power_v);
figure
plot(power_v, Valdepth50mms_02)
hold on
scatter(power,depth50_02, 'filled')
Cheers
Image Analyst
Image Analyst 2022-1-28
@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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