Extending regression lines beyond data span

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Maja Zdulska 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/814645-extending-regression-lines-beyond-data-span

评论： Scott MacKenzie 2021-5-8

Ice_North.txt

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Hi everyone,

I'm working on a code that would predict Arctic ice coverage during the rest of the 21st century, like so:

%load ice coverage data
data = load('Ice_North.txt');
%define variables
year = data(:,1);
data_month(:,1:12) = data(:,2:13); %a new matrix with monthly values only
%calculate the yearly average time series
yearData = nanmean(data_month,2); 
%plot yearly averaged time series
figure(1)
plot(year, yearData, 'LineWidth',2,'Color','b')
xlabel('Year')
ylabel('Sea ice coverage (milions of km^2)')
grid on
title('Annual average Arctic sea ice coverage')
%regression analysis
%linear
coeff1 = polyfit(year,yearData,1);
f1 = polyval(coeff1,year); 
hold on
plot(year,f1,'LineWidth',1.5,'Color','r')
%quadratic 
coeff2 = polyfit(year,yearData,2);
f2 = polyval(coeff2,year); 
hold on
plot(year,f2,'LineWidth',1.5,'Color','g')
legend('Data','Linear interpolation','Quadratic interpolation')