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Why dont Lagrange Multipliers have units

Posted Feb 25, 2012, 11:11 a.m. EST Parameters, Variables, & Functions Version 4.2a 3 Replies

John
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Comsol dutifully assigns units to things like pressure ("p"), dervied units like velocity "dl.u", etc.

But it doesn't assign units to Lagrange multiplers (like p_lm).

Why?

I have a more subtle reason for asking, I'm in the middle of working out if p_lm includes already contains an area term (i.e. is it flux * area) or not... I find the documentation confusing on this, but can work this out by running a quick case. But if the units were there already, then I would know immediately.

Thanks, John
3 Replies Last Post Feb 26, 2012, 3:05 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 25, 2012, 12:42 p.m. EST
Hi

excellent question, I have already asked COMSOL some time ago, about this, they told me they were preparing this for one of the future releases.

In the mean time the units of the LM's (fluxes) have always been in the doc, so, it's easy to add a *1[W/m^2] in HT or whatever is appropriate for you ;)

see doc Comsol User Guide 4.2a p460 table 7-2 "PHYSICS INTERFACE INTERPRETATION OF LAGRANGE MULTIPLIERS"

--
Good luck
Ivar
Hi excellent question, I have already asked COMSOL some time ago, about this, they told me they were preparing this for one of the future releases. In the mean time the units of the LM's (fluxes) have always been in the doc, so, it's easy to add a *1[W/m^2] in HT or whatever is appropriate for you ;) see doc Comsol User Guide 4.2a p460 table 7-2 "PHYSICS INTERFACE INTERPRETATION OF LAGRANGE MULTIPLIERS" -- Good luck Ivar
John
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Posted: 1 decade ago Feb 25, 2012, 12:58 p.m. EST
Yeh, what caught me out was my equation being solved is div (rho*kappa/mu grad p), so that p_lm has units of density*perm/viscosity*pressure/length.

I had missed the density term being inside the div, so I was expecting p_lm to have units of perm/viscosity*pressure/length

Regards, John
Yeh, what caught me out was my equation being solved is div (rho*kappa/mu grad p), so that p_lm has units of density*perm/viscosity*pressure/length. I had missed the density term being inside the div, so I was expecting p_lm to have units of perm/viscosity*pressure/length Regards, John
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 26, 2012, 3:05 a.m. EST
Hi

yes indeed its very easy to overlook such things, that is why I love the unit feature, would just appreciate that they arrive EVERYWHERE including material parameters, LMs, all plot scales, also time, and in the graphics window for the units of the graphics scale ;)

--
Good luck
Ivar
Hi yes indeed its very easy to overlook such things, that is why I love the unit feature, would just appreciate that they arrive EVERYWHERE including material parameters, LMs, all plot scales, also time, and in the graphics window for the units of the graphics scale ;) -- Good luck Ivar

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