Mathcad prime - does not answer

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The problem is the following calculations stays grey too and they are not refreshed.

 

-Formula calculation are not refreshed

-Quite often I have to kill the task because Mathcad does not answer

Any idea why this strange (and apparently random) behaviour ?

Unfortunately, no. I opened your sheet and recalculated it a few times but every time I had no difficulties to get a result from the symbolic evaluation of your function call to "get_LoadPinch(...)". I also changed one or two values to force a recalculation but again without any problems.

As Luc already noted you used an undefined variable (I) when you called "get_LoadPinch" and so the symbolic result of course depends on this unknown I.

BTW, because you name the formal function arguments when you define the function the very same as the actual arguments when you call it, its not clear from the picture you posted if you have the problem with the definition of the function or the later call to it.

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Another strange thing is that when it works, the last  formula does not simplify the units, although i defined mm:=10^-3m and gm=10^-3kg

Any clue of what is done done properly?

This time, yes. Two errors:

1) The (re)definition of the units is only in effect from the position you redefine them downwards. So you have to redefine the units for the symbolics before you use any of these units in your variable definitions as the symbolics otherwise won't use your redefinition.

2) When you redefine the units you must label the unit on the left hand side of the definition as "Unit" (by default this is indicated by a bold blue typeface). In your definition they are labelled as "Variable" and so are different from the units you use when you define variables.

I fixed the redefinitions and moved them in a collapsed region right at the very top of the sheet.

Also it helps to use the modifier "simplify" when you symbolically evaluate the function call.

Here is what I get:

As you can see you have some severe unit mismatch problems. The four summands have at least three, maybe even four (depends in the unit of I) different units and therefore sure can't be added.

If you fix these unit failures and provide a numerical value for I, you should be able to numerically evaluate (as opposed to the sometimes problematic symbolical evaluation) that function call, assign the result to a variable, etc.

EDIT: I had not realized that even though I used "open with Prime 9" the file would be opened in Prime 10. So the originally attached file was in P10 format. I  exchanged it now for a P9 version and to be on the safe side I downloaded the attached file and, yes, it correctly opened in Prime 9. But this time the last region with the evaluation of get_LoadPinch would not stop calculating and I had to kill the Prime process. Explanation? None other than "its Prime, a PTC developed software" 😉   Maybe when I tested it firsthand I inadvertently opened it in P10 and maybe P10 is a bit more stable. Or I simply had luck the first times. My guess is the latter 😉