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jaypee_66801-Visitor
1-Visitor
May 10, 2011
Solved

Solve Block Problems - Variable Undefined?

  • May 10, 2011
  • 2 replies
  • 12337 views

Hi there!

Wondering if anyone can help me out. I'm new to mathcad and having difficulty with solve blocks.

As far as I can see I'm entering all data correctly but keep getting an error variable undefined when I come to us the "find" function.

I'll attatch a couple of questions I cant get to work to see if anyone has any ideas.

Any pointers on this would be much appreciated.

Kind Regards,

John

Best answer by RichardJ

In the first equation you can't add the two terms in the denominator because kp and kins have different units.

Error messages from Mathcad solve blocks are essentially worthless, because there is only one: "This variable is undefined". You get this message regardless of what the actual error is. To get a real message select one of the equations and hit "=". If the equation has no problems it will evaluate to something (usually 0, since the two sides are not equal), otherwise you will get a more informative message.

2 replies

M
MikeArmstrong1-Visitor
1-Visitor
May 10, 2011

I think you need to look at your units. You have defined H and HW with units of kg/kg.

The units throughout your worksheet do not seem constant.

Mike

R
RichardJ19-Tanzanite
19-Tanzanite
May 10, 2011

In question 10 you have m raised to the power of 3*s^-1 (in two places). In question 11 your units do not match in equations 1 and 4.

J
jaypee_66801-VisitorAuthor
1-Visitor
May 10, 2011

Thank you very much! I couldn't see the wood for the trees! I was convinced it was a mathcad problem rather than an operator problem!

I have one more that I still cant get to work however. I've been looking at it for hours at I'm getting nowhere. I guess it's just practice though.

Any help with that would be much appreciated also. The trace error function thinks there is something wrong with one of my given functions? It should contain a temperature mulitplier apparently!

Kind Regards,

John

R
RichardJ19-TanzaniteAnswer
19-Tanzanite
May 10, 2011

In the first equation you can't add the two terms in the denominator because kp and kins have different units.

Error messages from Mathcad solve blocks are essentially worthless, because there is only one: "This variable is undefined". You get this message regardless of what the actual error is. To get a real message select one of the equations and hit "=". If the equation has no problems it will evaluate to something (usually 0, since the two sides are not equal), otherwise you will get a more informative message.

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