[petsc-users] Unconstrained optimization question

[Palmer, Bruce J]

Hi,

I’m trying to do an unconstrained optimization on a molecular scale problem. Previously, I was looking at an artificial molecular problem where all parameters were of order 1 and so the objective function and variables were also in the range of 1 or at least within a few orders of magnitude of 1.

More recently, I’ve been trying to apply this optimization to a real molecular system. Between Avogadro’s number (6.022e23) and Boltzmann’s constant (1.38e-16) combined with very small distances (1.0e-8 cm), etc. the objective function values and the values of the optimization variables have very large values (~1e86 and ~1e9, respectively). I’ve verified that the analytic gradients of the objective function that I’m calculating are correct by comparing them with numerical derivatives.

I’ve tried using the LMVM and Conjugate Gradient optimizations, both of which worked previously, but I find that the optimization completes one objective function evaluation and then declares that the problem is converged and stops. I could find a set of units where everything is approximately 1 but I was hoping that there are some parameters I can set in the optimization that will get it moving again. Any suggestions?

Bruce Palmer
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