[Coin-ipopt] Limit on MU

Dominique Orban Dominique.Orban at polymtl.ca
Wed Aug 3 14:31:35 EDT 2005

Oliveira, Ivan B wrote:

>Andreas - yes, the DTOL/10 limit is hard-coded into update_mu.f, and in
>fact overrides a previous statement based on QMUERRFAC (which I believe
>is currently prevented from affecting the algorithm):
>         mumin = QTOL/(2.d0*(QMUERRFAC+1.d0))
>         mumin = QTOL/10.d0

If you want to allow a smaller mu_min, you need to alter QMUERRFAC in 
PARAMS.DAT (the default value is 10) and you need, as Andreas suggested, 
to alter update_mu.f so that the first definition of mumin is used 
instead of the second (comment out the second).

This definition of mumin guarantees that once your barrier subproblem 
with mu=mumin has been solved, the final stopping test for the original 
problem will also be satisfied (in theory, you wouldn't need the 
division by 2 but it seems to help numerically).

Andreas: Since the two updates I sent you in relation to this are very 
simple, you may want to incorporate them into the Fortran version of 
IPOPT as well. It seems it will also be useful to others.


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