Radar Detection - MATLAB Simulations for Radar Systems Design - page 121

Listing 2.9. MATLAB Function Ðincomplete_gamma.mÑ
function [value] = incomplete_gamma ( vt, np)
% This function implements Eq. (2.67) to compute the Incomplete Gamma
Function
% This function needs "factor.m" to run
format long
eps = 1.000000001;
% Test to see if np = 1
if (np == 1)
value1 = vt * exp(-vt);
value = 1.0 - exp(-vt);
return
end
sumold = 1.0;
sumnew =1.0;
calc1 = 1.0;
calc2 = np;
xx = np * log(vt+0.0000000001) - vt - factor(calc2);
temp1 = exp(xx);
temp2 = np / (vt+0.0000000001);
diff = .0;
ratio = 1000.0;
if (vt >= np)
while (ratio >= eps)
diff = diff + 1.0;
calc1 = calc1 * (calc2 - diff) / vt ;
sumnew = sumold + calc1;
ratio = sumnew / sumold;
sumold = sumnew;
end
value = 1.0 - temp1 * sumnew * temp2;
return
else
diff = 0.;
sumold = 1.;
ratio = 1000.;
calc1 = 1.;
while(ratio >= eps)
diff = diff + 1.0;
calc1 = calc1 * vt / (calc2 + diff);
sumnew = sumold + calc1;
ratio = sumnew / sumold;
sumold = sumnew;