code: public void setC2(double c2)
      {
          if(c2 >= 1)
              throw new IllegalArgumentException("c2 must be less than 1, not " + c2);
          else if(c2 <= c1)
              throw new IllegalArgumentException("c2 must be greater than c1");
          this.c2 = c2;
      }
docs: Sets the constant used for the <i>curvature condition</i>
  p<sup>T</sup> &nabla;f(x+&alpha; p) &ge; c<sub>2</sub> p<sup>T</sup>&nabla;f(x)
  @param c2 the <i>curvature condition</i> constant