Field measurements

We can use GLU for all sorts of field measurements, such as determining the static potential from Coulomb gauge-fixed links, measuring the topological correlator (or the slab definition) or just measuring the topological charge. For examples of it in action you can consult https://arxiv.org/pdf/1809.09117 this paper.

These static potential and topological correlator are triggered via the

   MODE = CUTTING

Option in the input file followed by the

   CUTTYPE = {STATIC_POTENTIAL,TOPOLOGICAL_SUSCEPTIBILITY}

For the static potential

   MAX_T = 7

Gives the maximum length in time of the polyakov line and the field being read is expected to be in Coulomb gauge

A useful topology measurement

Whereas the topology via smearing is triggered by the

   MODE = SMEARING

There is a combination of configure options that I like to use

   --enable-GIVENS_APE
   --with-TOP_VALUE=45
   --enable-CLOVER_IMPROVE

In combination with 4D HYP smearing (0.75,0.5,0.25) for determining the field-definition of the topological charge. Here the routines will measure every 5th iteration of the topology from the clasically highly-improved tensor https://arxiv.org/abs/hep-lat/0203008 when the change in topology is small (and close to an integer) it will exit and give you the nearest integer. As more and more smearing destabilises instantons you need some way of quickly returning while the going is good.

Speaking of which you can also try these over-improved smearing routines if you like, there is an implementation available with the configure command

    --with-IMPROVED_STAPLE={IWASAKI,SYMANZIK,DBW2}
    --with-OVERIMPROVED_EPSILON={some number}

Once --enable-CLOVER_IMPROVE or IMPROVED_STAPLE or OVERIMPROVED_EPSILON are set these effect the staple calculations and field strength measurements in the gradient flow or the heatbath so be careful.