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01-06-2014
09:57 PM

01-06-2014
09:57 PM

Variable Undefined Error

Hi, I´m now starting to learn how to use Mathcad and I´m having troubles while using a Block Solve, it says I haven´t defined the variables even though I did, I´ll appreciate your help.

5 REPLIES 5

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01-07-2014
02:51 AM

01-07-2014
02:51 AM

Re: Variable Undefined Error

You can't always believe Mathcad's error messages. Right-click on the red part and select Trace error. Follow this and you will find it says "no solution found try changing TOL or initial guesses" (or words to that effect). However, you are asking for a solution to 14 unknowns, but only have 13 equations. You need another one.

Alan

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01-07-2014
03:20 AM

01-07-2014
03:20 AM

Re: Variable Undefined Error

Use please RT:= but not global definion!

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01-07-2014
02:10 PM

01-07-2014
02:10 PM

Re: Variable Undefined Error

Valery Ochkov wrote:

Use please RT:= but not global definion!

Why? There is nothing wrong with a global definition.

Its not necessary to use a global definition here but maybe the intent is to move the definition of RT downwards next to a result plot or something like this.

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01-07-2014
02:34 PM

01-07-2014
02:34 PM

Re: Variable Undefined Error

As Alan already stated your system is underdetermined, so it possibly may have an infinite number of solutions. But it also can be unsolvable if the equations demand the impossible.

I am not sure if you demand the impossible, but I noticed that if you disable the equations beginning with -31920+... and 70270+... Mathcad finds a solution. The same if you disable 149720+... and again 70270+...

Are you sure there exists a solution for the system as you typed it?

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01-07-2014
05:28 PM

01-07-2014
05:28 PM

Re: Variable Undefined Error

Thanks a lot, I will check the number of equations I see that I have more unknowns than equations.