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## prime 3.1 solve error  3-Visitor

## prime 3.1 solve error

I am currently using Prime 3.1 to solve a simple equation as given in my mathcad sheet.

My defined equation works to return correct values with the correct units. However using it to solve the equation for a single variable returns that there are no solutions.

Yet I should be able to get back a solution around 950 (verified by graphing in excel).

I am not too used to using this solve function in prime as usually I'd use the solve in Mathcad 15. Can someone more experienced just double check to see f I am doing anything incorrect ?

1 ACCEPTED SOLUTION

Accepted Solutions  24-Ruby V
(To:NovaStark)

Guess I just found a way to open P31 files in P30 (at least partially)

From what I see you first define a constant sigma.UTS and later you overwrite that value with a function of the very same name.

The function definitely should have a different name (I just added an underscore).

When I plot your function I see that there is a solution around 100 Delta°F, not 950

So maybe you used a different function in Excel.

While the symbolics still would not find an exact solution, the numeric root command does its job without problems: Guess a solve block with "find" would do the job as well.

5 REPLIES 5  24-Ruby V
(To:NovaStark)

Can you post a screenshot / pdf print of your file.

Am limited to P30 at the moment and so can't open your P31 file.  24-Ruby V
(To:NovaStark)

Guess I just found a way to open P31 files in P30 (at least partially)

From what I see you first define a constant sigma.UTS and later you overwrite that value with a function of the very same name.

The function definitely should have a different name (I just added an underscore).

When I plot your function I see that there is a solution around 100 Delta°F, not 950

So maybe you used a different function in Excel.

While the symbolics still would not find an exact solution, the numeric root command does its job without problems: Guess a solve block with "find" would do the job as well.  3-Visitor
(To:Werner_E)

Thanks!

I think you solved my error.

I made a mistake in the sheet, the 950 referred to solving for Srup (26 ksi or so).

Does this mean that for all functions f(x) = constant, I should use the root function rather than solve ?  24-Ruby V
(To:NovaStark)

The symbolic solver has its merits when it comes to solving equations with unknown variables symbolically. But it also had its limits. While it would normally switch to a float/numerical mode when it does not find an exact symbolic solution, it did not in case of your equation. Not sure why - it may have to do with the units as the symbolics is in no way unit aware. so ksi and Delta°F are treated as unknown variables.

When I remove the units and just solve for exponent=0 I get the five numerical solution of this fith order polynomial and one of them ist the 96.42 which we found via the root command. So I would suggest that as long as you are just after a numerical solution you use a numerical method like root or a solve block with Find.  24-Ruby III
(To:Werner_E)

Sorry one more not error but  