/**
* Returns the integral of 1/N(x) between t and g+t, calling either the getAnalyticalIntegral or
* getNumericalIntegral function as appropriate.
*/
private double getIntegral(double g, double t) {
if (g == 0.0) {
// integral value equals 0 if g=0
return 0.0;
}
if (demographicFunction.hasIntegral()) {
// Calculate integral analytically
return demographicFunction.getIntegral(t, t + g);
} else {
// Calculate integral numerically
return getNumericalIntegral(t, t + g);
}
}
/** Performs the trapezoid rule. */
private double doTrapezoid(int n, double low, double high, double lastS) {
double s;
if (n == 1) {
// On the first iteration s is reset
double demoLow = demographicFunction.getDemographic(low); // Value of N(x) obtained here
assert (demoLow > 0.0);
double demoHigh = demographicFunction.getDemographic(high);
assert (demoHigh > 0.0);
s = 0.5 * (high - low) * ((1.0 / demoLow) + (1.0 / demoHigh));
} else {
int it = 1;
for (int j = 1; j < n - 1; j++) {
it *= 2;
}
double tnm = it; // number of points
double del = (high - low) / tnm; // width of spacing between points
double x = low + 0.5 * del;
double sum = 0.0;
for (int j = 1; j <= it; j++) {
double demoX = demographicFunction.getDemographic(x); // Value of N(x) obtained here
assert (demoX > 0.0);
sum += (1.0 / demoX);
x += del;
}
s = 0.5 * (lastS + (high - low) * sum / tnm); // New s uses previous s value
}
return s;
}