code: public void setC1(double c1)
      {
          if(c1 <= 0)
              throw new IllegalArgumentException("c1 must be greater than 0, not " + c1);
          else if(c1 >= c2)
              throw new IllegalArgumentException("c1 must be less than c2");
          this.c1 = c1;
      }
docs: Sets the constant used for the <i>sufficient decrease condition</i>
  f(x+&alpha; p) &le; f(x) + c<sub>1</sub> &alpha; p<sup>T</sup>&nabla;f(x)
  <br>
  <br>
  This value must always be less than {@link #setC2(double) }
  @param c1 the <i>sufficient decrease condition</i>