<div class="gmail_quote">On Thu, Dec 29, 2011 at 08:10, Fatcharm <span dir="ltr"><<a href="mailto:wolfshow@gmail.com">wolfshow@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div id=":y4">We can see that the SNES Function norm is extremely large. I think it<br>
is because that the initial value for the unknown function H(X,T) is<br>
quite small and there is some terms like (1/H)(dH/dX) or<br>
(1/H^2)(dH/dX) in my equations.<br></div></blockquote><div><br></div><div>That may cause ill-conditioning, but you could still scale the equations so that the initial norm was of order 1. It shouldn't matter here though, because most methods are unaffected by scaling.</div>
<div><br></div><div>Are you computing an analytic Jacobian or using finite differencing?</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div id=":y4">
<br>
For "Linear solve did not converge due to DIVERGED_DTOL iterations<br>
3270", does this mean I should change the ksp_type?<br></div></blockquote></div><br><div>It's important to solve the linear systems before worrying about convergence rates for Newton methods. Try a direct solve on a small problem first, then read this</div>
<div><br></div><div><a href="http://scicomp.stackexchange.com/questions/513/why-is-my-iterative-linear-solver-not-converging">http://scicomp.stackexchange.com/questions/513/why-is-my-iterative-linear-solver-not-converging</a></div>
<div><br></div><div>If you fix the linear solve issues, but SNES is still not converging, read</div><div><br></div><div><a href="http://scicomp.stackexchange.com/questions/30/why-is-newtons-method-not-converging">http://scicomp.stackexchange.com/questions/30/why-is-newtons-method-not-converging</a></div>