<html><head></head><body>Criminy, that's disgusting. You implement options<br>
<br>
-term1 rhs -term2 lhs ...<br>
<br>
In your FormIFunction:<br>
<br>
if (term1 == LHS) { ... }<br>
<br>
and similarly in your FormRHSFunction.<br><br><div class="gmail_quote">On February 14, 2017 1:55:42 PM MST, Emil Constantinescu <emconsta@mcs.anl.gov> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail">On 2/14/17 2:33 PM, Zhang, Hong wrote:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> I think many users (including me) would like to start with academic examples, e.g. u_t=f(u)+g(u), when they try to learn PETSc TS solvers. This simple form allows for easy switch between all kinds of different integration methods.<br /></blockquote><br />Right, but then you can just write an if statement along the lines in <br />ex31.c: (this was before RHSJacobian and it's not intended for IMEX)<br /><br />TSGetType(ts,&time_scheme);<br />if ((!strcmp(time_scheme,TSEULER)) || (!strcmp(time_scheme,TSRK)) || <br />(!strcmp(time_scheme,TSSSP))) {<br />/* Explicit time-integration -> specify right-hand side function ydot = <br />f(y) */<br />TSSetRHSFunction(ts,NULL,RHSFunction,&ptype[0]);<br />} else if ((!strcmp(time_scheme,TSTHETA)) ||...<br /> (!strcmp(time_scheme,TSARKIMEX))) {<br /> /* Implicit time-integration -> specify left-hand side function <br />ydot-f(y) = 0 */<br /> /* and its Jacobian function */<br /> TSSetIFunction(ts,NULL,IFunction,&ptype[0]);<br /> TSSetIJacobian(ts,Jac,Jac,IJacobian,&ptype[0]);<br /> }<br /><br />This should not be a performance bottleneck. IFunction can be a wrapper <br />of the RHSFunction so not too much extra coding.<br /><br />Emil<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> Experienced users or experts who need to solve DAEs or complicate problems involving nontrivial mass matrix should be encouraged to try IFunction/IJacobian. Of course, we need better documentation to help them realize the switching is not always possible. Personally it took me a long time to get used to the IFunction business since I had been using u_t=f(u)+g(u) for a couple years before I jumped on PETSc. If we add support for this simple form, the learning curve would be less steep than it currently is.<br /><br /> Hong (Mr.)<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #ad7fa8; padding-left: 1ex;"> On Feb 14, 2017, at 11:55 AM, Jed Brown <jed@jedbrown.org> wrote:<br /><br /> Barry Smith <bsmith@mcs.anl.gov> writes:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #8ae234; padding-left: 1ex;"> Hence my suggestion to have TSSetLeftHandSideFunction() (or Jed's suggestion to have multiple Right Hand side functions) this will allow comparison of implicit, explicit, imex without recompiling (which we don't have currently) for the case with no mass matrix. With a mass matrix, unless we use mass lumping and have a TSSetMassMatrix() you cannot switch to full explicit, but that is due to mathematics, not the interface.<br /></blockquote><br /> Who in reality has a problem that looks like<br /><br /> u_t = f(u) + g(u) + h(u)<br /><br /> where it may make sense to move some of this to the left (implicit)?<br /> I'm concerned that this isn't natural for many applications so adding an<br /> interface would be solving a problem that doesn't really exist outside<br /> perhaps a few academic examples.<br /></blockquote></blockquote></pre></blockquote></div></body></html>