Custom Unit of Measure

[FB_10795922]

Good morning to all,

for my calculation I've to deal with badly conditioned matrices. The matrices includes terms with its own unit of measure. The bad conditioning is coming (also after some simple numerical tests) from the very different order of magnitude of the terms and it could be reduced introducing, new, custom unit of measures (such as for example MegaNewton for example). I know how to introduce custom unit of measures in input. BUT what I want is that for an entire spreadsheet (or even a region) a custom unit system is used; said differently I want that the results are in the custom unit of measures: how can I do? Many thanks in advance 

[terryhendicott]

Hi,

Are you making structural stiffness matrices?

Cheers

Terry

[FB_10795922]

....close to it....transfer matrix for modal analysis...

[Werner_E · Accepted solution]

As far as I know things like default custom units are planned by PTC for some future version.

At the time being such a feature is not available and you would have to manually change the units of your results, which, unfortunately is also not possible to do if a matrix contains values of different dimensions.

BTW, using custom units like MN would not affect the bad conditioning because internally Prime will always calculate with values in the default SI unit.

[Cornel]

Is this? Mathcad Prime 11 was release few days ago...

[FB_10795922]

...it really seems what I'm looking for.....BUT, unfortunately I'm working with Prime9 version

[FB_10795922]

...in facts what you describe is what happened to me defining the input with custom unit of measure. I thought there was a work around...for memo I'm using Prime9 version

[LucMeekes]

Isn't 'Custom Units' implemented in Prime 11?

Luc

[FB_10795922]

Thanks nice to know but I'm still working with Prime9....

[Werner_E]

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@LucMeekes wrote:

Isn't 'Custom Units' implemented in Prime 11?

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You (and Cornel) seem to be right that its already implemented in P11. Have not yet installed P11 and there seems to be no comprehensive "Whats new in P11" documentation online (or I hadn't looked hard enough for it).

I guess that its for display purposes only and will not affect internal calculations!? That means that with  very large or very tiny magnitudes we will still see the problematic behaviour with "match" and "lookup" and maybe also when solving bad conditioned systems of equations?

EDIT: Incidentally, this is what I was referring to with the problematic behavior of “match”, etc.:

Is the effect the same in P11 when the custom time unit is set to microseconds?

[LucMeekes]

Can't check. It's Express for me, and all, yes ALL, new items in Prime 11 are behind that fence for me.

So the IsRange function that I deerly missed is also unavailable.

Luc

[Cornel]

Me neither, I don't have yet Prime 11 installed (since my company hasn't made this latest version available yet, but they should introduce it in a few weeks, most probable I am expecting, and then I can see how Prime 11 is working, i.e. how the 'improvements' of this version feel...(though I don't expect it to be something special or too much powerfull))

[DJNewman]

Official what's new documentation: https://support.ptc.com/help/mathcad/r11.0/en/#page/PTC_Mathcad_Help/whatsNewMathcadPrime.html

[terryhendicott]

[Werner_E]

Thanks, I know about the workarounds by either getting rid of the units as you did or by setting a lower TOL value or by using your own comparison function:

Getting rid of the units also can be a bit tricky and error-prone if you think of "vlookup" or "lookup", where the results are expected in the correct unit.

However, I would have been interested to know whether it works in P11 without these tricks if you use a custom unit system with microseconds as its default time unit.

Do you use Prime 11 and does your answer mean that nonetheless its still necessary to use workarounds??

[terryhendicott]

Hi Werner,

Still on Prime 10.

Cheers

Terry

[FB_10795922]

One thing more, LucMees: am I right or following what you reproduce, custom unit system should be created OUTSIDE the MathCAD graphic interface and it will appear in the graphic interface? It seems to me to have read something similar BUT I was "shy" to modify an external file (even creating an copy of the file BEFORE modification)...THANKS

[Werner_E]

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@FB_10795922 wrote:

One thing more, LucMees: am I right or following what you reproduce, custom unit system should be created OUTSIDE the MathCAD graphic interface and it will appear in the graphic interface? It seems to me to have read something similar BUT I was "shy" to modify an external file (even creating an copy of the file BEFORE modification)...THANKS

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Thank you!

Not very detailed and comprehensive, but at least something.
And sure better than having to laboriously search for the changes one by one in the KB, as was the case with 10.0.1.0.