../../sf_beta/beta_derivative.html" title="Derivative of the Incomplete Beta Function">ibeta_derivative</a>(v1
                    / 2, v2 / 2, v1 * x / (v2 + v1 * x))
                  </p>
                  <p>
                    with y = (z * v1 - x * v1 * v1) / z<sup>2</sup>
                  </p>
                  <p>
                    and z = v2 + v1 * x
                  </p>
                  <p>
                    The first of these is used for v1 * x &gt; v2, otherwise the
                    