private void quadraticBacktrack(DoubleArray p, System.Func <DoubleArray, DoubleArray> function, DataBundle data)
{
double lambda0 = data.Lambda0;
double g0 = data.G0;
double lambda = Math.Max(0.01 * lambda0, g0 * lambda0 * lambda0 / (data.G1 + g0 * (2 * lambda0 - 1)));
data.swapLambdaAndReplace(lambda);
updatePosition(p, function, data);
}
private void cubicBacktrack(DoubleArray p, System.Func <DoubleArray, DoubleArray> function, DataBundle data)
{
double temp1, temp2, temp3, temp4, temp5;
double lambda0 = data.Lambda0;
double lambda1 = data.Lambda1;
double g0 = data.G0;
temp1 = 1.0 / lambda0 / lambda0;
temp2 = 1.0 / lambda1 / lambda1;
temp3 = data.G1 + g0 * (2 * lambda0 - 1.0);
temp4 = data.G2 + g0 * (2 * lambda1 - 1.0);
temp5 = 1.0 / (lambda0 - lambda1);
double a = temp5 * (temp1 * temp3 - temp2 * temp4);
double b = temp5 * (-lambda1 * temp1 * temp3 + lambda0 * temp2 * temp4);
double lambda = (-b + Math.Sqrt(b * b + 6 * a * g0)) / 3 / a;
lambda = Math.Min(Math.Max(lambda, 0.01 * lambda0), 0.75 * lambda1); // make sure new lambda is between 1% & 75% of old value
data.swapLambdaAndReplace(lambda);
updatePosition(p, function, data);
}