EES (Engineering Equation Solver)

[andradesilva]

Hi,

I derived a 4th degree equation that I am using in EES (Engineering Equation Solver). The system solves very well, but when I try to add my equation, which is a 4th degree equation, the software gives the error that I show in the picture that attach to this post. The equation is A = 102369 - 3.06e11*B^4
The unknown is B. A is a known scalar, and I checked its value. It's correct. The equation is well derived, I already checked it. The .EES file runs without problems if I change the equation to a 1st degree one, resulting, of course, in totally wrong results.

Can someone tell me what can be going on?
Thank you,
Best regards,

 

[davefitz]

I am not sure, but in general systems of equations can be solved in a stable manner if each equation is expressed to a power less than or equal to 1. Try rewriting the equation as B=(102369-A)^.25

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[Latexman]

I saw no picture attached.

A syntax error? Try A = 102369 - 3.06e11*B**4

Is it 3.06E11 or 3.06E-11?

Good Luck,
Latexman

 

[IRstuff]

Conversely

B = {(102369 - A)/(3.06e11)}^0.25, or **0.25 if that's the syntax

Mathcad's solver has occasionally burped and needed to get a different expression of the equations to get it to work.

I think that linearizing the unknown usually makes the solver happier. Anything higher order than 2 results in multiple roots that can cause problems if they are too close together.


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[chicopee]

IRstuff conversed equation is correct but be careful about A not being greater than 102,369 which may explain the error in EES.
It seems that the OP's equation was derived from a regression analysis; is that correct?

 

[andradesilva]

Hi!

Thank you very much for the help.


Mr. Davefitz:

I revised the equation to the one you suggested. I got this error: Run 1: This equation atttempts to raise a negative number to a non-integer power


Mr. Latexman

I tried to use ** instead of ^ for the exponent. Same error appears in both cases: Run 1: This equation atttempts to raise a negative number to a non-integer power


Mr. IRSstuff

I think that if { and/or } are used elsewhere, the characters in-between are not recognized by the EES solver as equations. I tried it and I get a sintax error.


Mr. chicopee,

Yes, this equation was derived from data obtained from experimental tests in the company I work.


Are there any other suggestions?

Thank you all once again,
Best regards,

 

[IRstuff]

Is A larger than 102369, then? That would seem to be problematic. Can you start A with a smaller value? Have you graphed all the equations to see if they make sense?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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