Hellow,<div><br></div><div>I have found two bugs in the codes, and I listed them in the attachment.</div><div><br></div><div>I have a question about why the backward differentiation formula starts after&nbsp;m_pressureCalls&gt;2, in function&nbsp;</div><div>void Nektar::Extrapolate::AccelerationBDF(Array&lt; OneD, Array&lt; OneD, NekDouble &gt; &gt; &amp; array).</div><div>Since when&nbsp;<span style="line-height: 16.8px;">m_pressureCalls=2, we can already get a first order accuracy result.</span><span style="line-height: 1.2;">&nbsp;</span></div><div><br></div><div><br></div><div>thanks</div><div><br></div><div>Ankang</div>