So I've fitted a linear trend to my data and calculated R^2 in two different ways (in Matlab), one is using `corrcoef` and the other is "by hand". These return different results and both seem to make sense, so I'm not sure why that is. My methods are as follows, with `x` being the number of years and `y` my values:

    (1)
    rsq1 = corrcoef(x, y);

    (2)
    %// fitting the model
    p = polyfit(x,y);
    yfit = polyval(p,x);

    %// calculating R^2
    yresid = y - yfit;
    SSresid = sum(yresid.^2);
    SStotal = (length(y)-1) * var(y);
    rsq2 = 1 - SSresid/SStotal;

Since I'm very new to this I can't seem to figure out why `rsq1` and `rsq2` are different. I have a feeling I'm missing something obvious... does anyone have an idea?

Thanks for any help!