How to fix line that exceeds number of array elements(1)

Question

Victoria Morrison 2021-1-10

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回答： Walter Roberson 2021-1-10

file = readmatrix('CO2.xlsx'); % given file
year = file(:,1);
month = file(:,2);
levelCO2 = file(:,3);
crctCO2 = file(:,4);
i = 1;
for x = [1959:2018] % years to be evaluated
    for m = [1:12] % all 12 months
        b = year == x & month == m; 
        avgCO2(i) = mean(file(b(i),4)); % mean CO2 levels from 1959-2018
        prct_inc(i+1) = ((avgCO2(i+1)-avgCO2(i))/avgCO2(i))*100; %equation for year-to-year percent increase of CO2 levels  
        Time2(i) = x + m/12;
        i = i + 1;
    end
end

Index exceeds the number of array elements (1).

Error in (line 34)

prct_inc(i+1) = ((avgCO2(i+1)-avgCO2(i))/avgCO2(i))*100;

How do I fix this?

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Answer 1

Cris LaPierre 2021-1-10

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The error is with avgCO2(i+1). The value at i+1 has not been defined yet, hence the error.

You could try defining a value for avgCO2(1) before your nested for loops (perhaps it's 0), then start your index counter at i=2. Rewrite your formula to look backwards instead of forwards.

prct_inc(i) = ((avgCO2(i)-avgCO2(i-1))/avgCO2(i-1))*100;

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Answer 2

Walter Roberson 2021-1-10

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You use the average CO2 for the year after the current one, before you have stored anything there.

        b = year == x & month == m; 
        avgCO2(i) = mean(file(b(i),4)); % mean CO2 levels from 1959-2018

What is your intention about what you are taking the mean of? mean over the entire year would require mean(levelC02(year==x)) and should be done before the month loop.