/// <summary>
/// Computes the definite integral within the borders a and b.
/// </summary>
/// <param name="a">Left integration border.</param>
/// <param name="b">Right integration border.</param>
/// <returns></returns>
public double Integrate(double a, double b)
{
double[] buf = new double[Degree + 2];
buf[0] = 0; // this value can be arbitrary, in fact
for (int i = 1; i < buf.Length; i++)
buf[i] = Coefficients[i - 1] / i;
Polynomial p = new Polynomial(buf);
return (p.Evaluate(b) - p.Evaluate(a));
}
public static Polynomial operator *(Polynomial p, Polynomial q)
{
int degree = p.Degree + q.Degree;
Polynomial r = new Polynomial();
for (int i = 0; i <= p.Degree; i++)
for (int j = 0; j <= q.Degree; j++)
r += (p.Coefficients[i] * q.Coefficients[j]) * Monomial(i + j);
return r;
}
/// <summary>
/// Computes the roots of polynomial p via Weierstrass iteration.
/// </summary>
/// <param name="p">Polynomial to compute the roots of.</param>
/// <param name="tolerance">Computation precision; e.g. 1e-12 denotes 12 exact digits.</param>
/// <param name="max_iterations">Maximum number of iterations; this value is used to bound
/// the computation effort if desired pecision is hard to achieve.</param>
/// <returns></returns>
public static double[] Roots(Polynomial p, double tolerance, int max_iterations)
{
Polynomial q = Normalize(p);
double[] z = new double[q.Degree]; // approx. for roots
double[] w = new double[q.Degree]; // Weierstraß corrections
// init z
for (int k = 0; k < q.Degree; k++)
//z[k] = (new Complex(.4, .9)) ^ k;
z[k] = Math.Exp(2 * Math.PI * k / q.Degree);
for (int iter = 0; iter < max_iterations
&& MaxValue(q, z) > tolerance; iter++)
for (int i = 0; i < 10; i++)
{
for (int k = 0; k < q.Degree; k++)
w[k] = q.Evaluate(z[k]) / WeierNull(z, k);
for (int k = 0; k < q.Degree; k++)
z[k] -= w[k];
}
// clean...
for (int k = 0; k < q.Degree; k++)
{
z[k] = Math.Round(z[k], 12);
}
return z;
}
/// <summary>
/// Factorizes polynomial to its linear factors.
/// </summary>
/// <returns></returns>
public FactorizedPolynomial Factorize()
{
// this is to be returned
FactorizedPolynomial p = new FactorizedPolynomial();
// cannot factorize polynomial of degree 0 or 1
if (this.Degree <= 1)
{
p.Factor = new Polynomial[] { this };
p.Power = new int[] { 1 };
return p;
}
double[] roots = Roots(this);
Polynomial[] factor = new Polynomial[roots.Length];
int[] power = new int[roots.Length];
power[0] = 1;
factor[0] = new Polynomial(new double[] { -Coefficients[Degree] * (double)roots[0], Coefficients[Degree] });
for (int i = 1; i < roots.Length; i++)
{
power[i] = 1;
factor[i] = new Polynomial(new double[] { -(double)roots[i], 1 });
}
p.Factor = factor;
p.Power = power;
return p;
}
/// <summary>
/// Computes the greatest value |p(z_k)|.
/// </summary>
/// <param name="p"></param>
/// <param name="z"></param>
/// <returns></returns>
public static double MaxValue(Polynomial p, double[] z)
{
double buf = 0;
for (int i = 0; i < z.Length; i++)
{
if (Math.Abs(p.Evaluate(z[i])) > buf)
buf = Math.Abs(p.Evaluate(z[i]));
}
return buf;
}
/// <summary>
/// Normalizes the polynomial, e.i. divides each coefficient by the
/// coefficient of a_n the greatest term if a_n != 1.
/// </summary>
public static Polynomial Normalize(Polynomial p)
{
Polynomial q = Clean(p);
if (q.Coefficients[q.Degree] != 1)
for (int k = 0; k <= q.Degree; k++)
q.Coefficients[k] /= q.Coefficients[q.Degree];
return q;
}
/// <summary>
/// Integrates given polynomial p.
/// </summary>
/// <param name="p"></param>
/// <returns></returns>
public static Polynomial Integral(Polynomial p)
{
double[] buf = new double[p.Degree + 2];
buf[0] = 0; // this value can be arbitrary, in fact
for (int i = 1; i < buf.Length; i++)
buf[i] = p.Coefficients[i - 1] / i;
return new Polynomial(buf);
}
public static Polynomial[] GetStandardBase(int dim)
{
if (dim < 1)
throw new ArgumentException("Dimension expected to be greater than zero.");
Polynomial[] buf = new Polynomial[dim];
for (int i = 0; i < dim; i++)
buf[i] = Monomial(i);
return buf;
}
/// <summary>
/// Expands factorized polynomial p_1(x)^(k_1)*...*p_r(x)^(k_r) to its normal form a_0 + a_1 x + ... + a_n x^n.
/// </summary>
/// <param name="p"></param>
/// <returns></returns>
public static Polynomial Expand(FactorizedPolynomial p)
{
Polynomial q = new Polynomial(1);
for (int i = 0; i < p.Factor.Length; i++)
{
for (int j = 0; j < p.Power[i]; j++)
q *= p.Factor[i];
q.Clean();
}
return q;
}
/// <summary>
/// Differentiates given polynomial p.
/// </summary>
/// <param name="p"></param>
/// <returns></returns>
public static Polynomial Derivative(Polynomial p)
{
double[] buf = new double[p.Degree];
for (int i = 0; i < buf.Length; i++)
buf[i] = (i + 1) * p.Coefficients[i + 1];
return new Polynomial(buf);
}
/// <summary>
/// Removes unncessary leading zeros.
/// </summary>
/// <param name="p"></param>
/// <returns></returns>
public static Polynomial Clean(Polynomial p)
{
int i;
for (i = p.Degree; i >= 0 && p.Coefficients[i] == 0; i--) ;
double[] coeffs = new double[i + 1];
for (int k = 0; k <= i; k++)
coeffs[k] = p.Coefficients[k];
return new Polynomial(coeffs);
}