Extending regression lines beyond data span

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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')
I would like to extend both linear and quadratic interpolations, so that they reach up to, for example 2100. Any advice on how to do that?
All the best,
Maja
  5 Comments
Scott MacKenzie
Scott MacKenzie on 8 May 2021
Great. Thanks very much. Very nice work.

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