double EwaldgpuForce::tune_rcut(double accuracy, double precision, double alpha, double V, double q_sqr, int N)
{
double rcut_low=0.0;
double rcut_high=0.5 * std::max(box_l[0],std::max(box_l[1],box_l[2]));
double rcut_guess;
double fkt_low;
double fkt_high;
double fkt_guess;
// Find rcut with given K in k-space error estimate via bisection
fkt_low = error_estimate_r(q_sqr, N, rcut_low, V, alpha, accuracy);
fkt_high = error_estimate_r(q_sqr, N, rcut_high, V, alpha, accuracy);
if (fkt_low*fkt_high > 0.0)
{
return -1; // Value unusable
}
do
{
rcut_guess = 0.5 *(rcut_low + rcut_high);
fkt_guess = error_estimate_r(q_sqr, N, rcut_guess, V, alpha, accuracy);
if (fkt_low*fkt_guess < 0.0) rcut_high = rcut_guess;
else rcut_low = rcut_guess;
} while (fabs(rcut_low-rcut_high) > precision);
return 0.5 *(rcut_low + rcut_high);
}
double EwaldgpuForce::tune_rcut(double accuracy, double precision, double alpha, double V, double q_sqr, int N)
{
double rcut_low=std::numeric_limits<double>::epsilon();
/* Limit maximal cutoff to 10000 particles in rcut sphere. */
double rcut_high=std::min(std::min(box_l[0],std::min(box_l[1],box_l[2])), pow((3000.0*V)/(4.0*3.14159*N), 1.0/3.0));
double rcut_guess;
double fkt_low;
double fkt_high;
double fkt_guess;
// Find rcut with given K in k-space error estimate via bisection
fkt_low = error_estimate_r(q_sqr, N, rcut_low, V, alpha, accuracy);
fkt_high = error_estimate_r(q_sqr, N, rcut_high, V, alpha, accuracy);
if (fkt_low*fkt_high > 0.0)
{
return -1; // Value unusable
}
do
{
rcut_guess = 0.5 *(rcut_low + rcut_high);
fkt_guess = error_estimate_r(q_sqr, N, rcut_guess, V, alpha, accuracy);
if (fkt_low*fkt_guess < 0.0) rcut_high = rcut_guess;
else rcut_low = rcut_guess;
} while (fabs(rcut_low-rcut_high) > precision);
return 0.5 *(rcut_low + rcut_high);
}
