C</em></span> grows quickly
      and &#949;<sup>k/k+1</sup> approaches &#949; slowly, we can see there is a compromise
      between high-order accuracy and conditioning of the difference quotient. In
      practice we have found that <span class="emphasis"><em>k=6</em></span> seems to be a good compromise
      between the two (and have made this the default), but users are encouraged
      to examine the error estimates to choose an optimal order of accuracy for the
      given problem.
    </p>
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