package com.dwave.math;

public final class StiffMethods {

  private StiffMethods() {}

  /**
   *  Fourth-order Rosenbrock step for integrating stiff o.d.e.'s, with monitoring of local
   *  truncation error to adjust stepsize. Input are the dependent variable vector <code>y[1..n]</code>
   *  and its derivative <code>dydx[1..n]</code> at the starting value of the independent varable
   *  <code>x</code>. Also input are the stepsize to be attempted <code>htry</code>, the required
   *  accuracy <code>eps</code>, and the vector <code>yscal[1..n]</code> against which
   *  the error is scaled. On output, <code>y</code> and <code>x</code> are replaced by their
   *  new values, <code>hdid</code> is the stepsize that was actually accomplished, and
   *  <code>hnext</code> is the estimated next stepsize. <code>derivs</code> is the
   *  user-supplied routine that computes the derivatives of the right-hand side with
   *  respect to <code>x</code>, while <code>jacobn</code>(a fixed name) is a user-supplied
   *  routine that computes the Jacobi matrix of derivatives of the right-hand side with respect
   *  to the components of <code>y</code>.
   */
  public static void stiff() {
    int MAXTRY = 40;
    float SAFETY = 0.9F,
          GROW = 1.5F,
          PGROW = -0.25F,
          SHRNK = 0.5F,
          PSHRNK = -1F/3F,
          ERRCON = 0.1296F,
          gam = 1f/2f,
          a21 = 2f,
          a31 = 48f/25f,
          a32 = 6f/25f,
          c21 = -8f,
          c31 = 12f/5f,
          c41 = -112f/125f,
          c42 = -54f/125f,
          c43 = -2f/5f,
          b1 = 19f/9f,
          b2 = 1f/2f,
          b3 = 25f/108f,
          b4 = 125f/108f,
          e1 = 17f/54f,
          e2 = 7f/36f,
          e3 = 0f,
          e4 = 125f/108f,
          c1x = 1f/2f,
          c2x = -3f/2f,
          c3x = 121f/50f,
          c4x = 29f/250f,
          a2x = 1f,
          a3x = 3f/5f;
  }
}