adaptAlpha()

void syten::MPS::DMRG::Worker::adaptAlpha	(	SRDef const	preTrunc,
		SRDef const	postTrunc
	)

Adapt the mixing factor alpha based on energy gain.

Parameters

preTrunc	energy prior to truncation, after solution
postTrunc	energy after truncation

Also uses conf.lastEnergy for the energy before the truncation.

The idea is that we want to keep the energy loss during truncation at some 30% of the energy gain during optimisation and adapt conf.alpha accordingly, as it controls the strength of the perturbation.

References syten::abs(), std::isnan(), std::max(), and std::min().

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