double Polynomial::newtonRaphson(double guess){
Polynomial deriv = this->derivative();
double nextGuess = guess;
double fVal = this->evaluate(nextGuess);
while(std::abs(fVal) > .000000001){
if(0 == deriv.evaluate(nextGuess)){ nextGuess += 1; }
nextGuess -= (fVal)/(deriv.evaluate(nextGuess));
fVal = this->evaluate(nextGuess);
}
return nextGuess;
}
vector<CoeffT> Polynomial<CoeffT>::roots(size_t num_iterations, CoeffT ztol) const
{
assert(c.size() >= 1);
size_t n = c.size() - 1;
// initial guess
vector<complex<CoeffT>> z0(n);
for (size_t j = 0; j < n; j++) {
z0[j] = pow(complex<double>(0.4, 0.9), j);
}
// durand-kerner-weierstrass iterations
Polynomial<CoeffT> p = this->normalize();
for (size_t k = 0; k < num_iterations; k++) {
complex<CoeffT> num, den;
for (size_t i = 0; i < n; i++) {
num = p.evaluate(z0[i]);
den = 1.0;
for (size_t j = 0; j < n; j++) {
if (j == i) { continue; }
den = den * (z0[i] - z0[j]);
}
z0[i] = z0[i] - num / den;
}
}
vector<CoeffT> roots(n);
for (size_t j = 0; j < n; j++) {
roots[j] = abs(z0[j]) < ztol ? 0.0 : real(z0[j]);
}
sort(roots.begin(), roots.end());
return roots;
}
Intervals PolynomialIntervalSolver::findPolyIntervals(const Polynomial &poly)
{
const double eps = 1e-8;
int leadcoeff=0;
std::vector<Interval> empty;
std::vector<Interval> all;
all. push_back(Interval(-std::numeric_limits<double>::infinity(),
std::numeric_limits<double>::infinity()));
const std::vector<double> &coeffs = poly.getCoeffs();
int deg = coeffs.size()-1;
for(int i=0; i<(int)coeffs.size(); i++)
assert(!isnan(coeffs[i]));
// get rid of leading 0s
// for(leadcoeff=0; leadcoeff < (int)coeffs.size() && fabs(coeffs[leadcoeff]) < eps; leadcoeff++)
// {
// deg--;
// }
// check for the zero polynomial
if(deg < 0)
{
return Intervals(empty);
}
// check for constant polynomial
if(deg == 0)
{
double val = poly.evaluate(0);
if(val > 0)
{
return Intervals(all);
}
return Intervals(empty);
}
// nonconstant polynomial... rpoly time!!!
assert(deg <= 6);
double zeror[6];
double zeroi[6];
int numroots = rf.rpoly(&coeffs[leadcoeff], deg, zeror, zeroi);
std::vector<double> roots;
for(int i=0; i<numroots; i++)
if( fabs(zeroi[i]) < eps )
roots.push_back(zeror[i]);
// no roots: check at 0
if(roots.size() == 0)
{
double val = poly.evaluate(0);
if(val > 0)
return Intervals(all);
return Intervals(empty);
}
std::sort(roots.begin(), roots.end());
std::vector<Interval> intervals;
for(int i=0; i<(int)roots.size(); i++)
{
if(i == 0)
{
//check poly on (-inf, r)
double t = roots[i]-1;
double val = poly.evaluate(t);
if(val > 0)
{
intervals.push_back(Interval(-std::numeric_limits<double>::infinity(),
roots[i]));
}
}
if(i == (int)roots.size()-1)
{
//check poly on (r, inf)
double t = roots[i]+1;
double val = poly.evaluate(t);
if(val > 0)
{
intervals.push_back(Interval(roots[i],
std::numeric_limits<double>::infinity()));
}
}
if(i < (int)roots.size()-1)
{
// check poly on (r, r+1)
double t = 0.5*(roots[i]+roots[i+1]);
double val = poly.evaluate(t);
if(val > 0)
{
intervals.push_back(Interval(roots[i],
roots[i+1]));
}
}
}
return Intervals(intervals);
}
