Questions on Rayleigh Damping commands

[FBeckwith]

I'd like to know at what point is the damping matrix generated in the domain? I'm looking at turning off damping at certain nodes and/or elements and would like to know what precedence the rayleigh command and -doRayleigh flags have over each other.

It appears the commands for building the damping matrix are:
1) rayleigh command (rayleigh $alphaM $betaK $betaKinit $betaKcomm)
2) region command with the -rayleigh flag and coefficients (region $regTag ... <-rayleigh $alphaM $betaK $betaKinit $betaKcomm>)
3) certain zeroLength and truss elements with -doRayleigh flag (zeroLength ...<-doRayleigh $rFlag>...)

The wiki states the rayleigh command overwrites any existing damping commands. This makes me think that if I'd like to specify different rayleigh coefficients (alpha & beta) using the region command, it needs to come after calling the rayleigh command for them to take effect (or else it is overwritten). Is this correct?

Also, I'm pretty sure the -doRayleigh flag on certain elements control whether that element contribute to the damping matrix via stiffness proportional damping (using whatever coefficient is assigned to it either by "rayleigh" command or the "region" command with different -rayleigh coefficients). Is this correct?

Thanks in advance!

[fmk]

the damping is turned on at the elements and nodes. all elements and nodes which are in place before the rayleigh command is issued will use the the rayleigh factors.

yes, the region command wouldneed to be issued after the rayleigh command.

yes. the ZeroLeng and Truss elements were originally written not to include rayleigh damping. so as not to mess anybodies original scrip we had to add this option to include rayleigh damping with tose elements.

[fbeckwit]

Much appreciated, thank you for the response.

[civil]

for computing Rayleigh Damping 2 mode should be used. what are these mode?
are they first mode and nth mode which Tn=0.1 T1?