// Calculate function required for the approximation.
bigfloat AlgRemez::func(const bigfloat x) {
bigfloat z = (bigfloat)power_num / (bigfloat)power_den;
bigfloat y;
if (x == (bigfloat)1.0) y = (bigfloat)1.0;
else y = pow_bf(x,z);
if (a_length > 0) {
bigfloat sum = 0l;
for (int j=0; j<a_length; j++) sum += a[j]*pow_bf(x,a_power[j]);
return y * exp_bf(sum);
} else {
return y;
}
}
// Calculate function required for the approximation
bigfloat AlgRemez::func(const bigfloat x) {
char *fname = "func(bigfloat)";
// VRB.Func(cname,fname);
bigfloat z,y,dy,f=1l,df;
switch (approx_type) {
case RATIONAL_APPROX_POWER:
case RATIONAL_APPROX_ZERO_POLE:
z = x;
break;
case RATIONAL_APPROX_QUOTIENT:
z = x/(x+delta_m);
break;
default:
ERR.General(cname,fname,"ApproxType %d not implemented\n", approx_type);
}
#ifdef USE_MPFR
if (approx_type == RATIONAL_APPROX_POWER ||
approx_type == RATIONAL_APPROX_QUOTIENT) {
if (z == (bigfloat)1.0) return (bigfloat)1.0;
else return pow_bf(z,(bigfloat)power_num / (bigfloat)power_den);
}
#endif
// initial guess to accelerate convergance
y = (bigfloat)pow((double)z,(double)((bigfloat)1l/(bigfloat)power_den));
while (abs_bf(f)>(bigfloat)1l/pow_bf((bigfloat)10,prec)) { // approx good to 10^(-prec)
f = pow_bf(y,power_den) - z;
df = (bigfloat)power_den*pow_bf(y,power_den-1);// need power_den-1 because of diff
dy = f/df;
y -= dy;
}
if (approx_type == RATIONAL_APPROX_POWER ||
approx_type == RATIONAL_APPROX_QUOTIENT) {
return pow_bf(y,power_num);
} else if (approx_type == RATIONAL_APPROX_ZERO_POLE) {
if (power_num > power_den) return pow_bf(y,power_num-power_den);
else return (bigfloat)1.0/pow_bf(y,power_den-power_num);
}
}
