dfapiece.m

function [alpha1, alpha2, alpha3, alpha1flag, alpha2flag, alpha3flag] = dfapiece(d,p)

m = length(d);
tempY1 = [];
tempX1 = [];
tempY2 = [];
tempX2 = [];
tempY3 = [];
tempX3 = [];

for i = 1:m
    if (d(i) >= 10) && (d(i) <= 30) % 10 <= n <= 30
        tempY1(end+1) = p(i);
        tempX1(end+1) = d(i);
    end
    if (d(i) >= 30) && (d(i) <= 300) % 30 <= n <= 300
        tempY2(end+1) = p(i);
        tempX2(end+1) = d(i);
    end
    if (d(i) >= 300) % 300 <= n
        tempY3(end+1) = p(i);
        tempX3(end+1) = d(i);
    end
end

if length(tempX1) > 1
    alpha1 = polyfit(log10(tempX1),log10(tempY1),1);
    alpha1 = alpha1(1);
    alpha1flag = 1;
else
    alpha1 = 0;
    alpha1flag = 0;
end

if length(tempX2) > 1
    alpha2 = polyfit(log10(tempX2),log10(tempY2),1);
    alpha2 = alpha2(1);
    alpha2flag = 1;
else
    alpha2 = 0;
    alpha2flag = 0;
end
 
if length(tempX3) > 1
    alpha3 = polyfit(log10(tempX3),log10(tempY3),1);
    alpha3 = alpha3(1);
    alpha3flag = 1;
else
    alpha3 = 0;
    alpha3flag = 0;
end