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Find Function

ptc-5003994
1-Newbie

Find Function

I am trying to use the find function to solve for two variables from two equations. It says my variable is undefined, however. Is this because I included units in some of my known variables?

1 ACCEPTED SOLUTION

Accepted Solutions

While you are sorting out how to attach a file (the forum software used here unfortunately is quite confusing and not user friendly defaulted) I think it dawned to me what the problem could be.

You wrote about two equations in two variables.

If these two varaibles have different units and you try to assign the result of Find to a single variable name you run into troubles, because Mathcad would not allow different units in a vector/matrix.

But there is a way out - see attached.

FindWithUnits.png

View solution in original post

13 REPLIES 13

I don't see any usage of a solve block which failed nor any equations to solve?

Sorry, wrong file attached. Now I can't seem to see how to attach a new file... Sorry I'm new here

I tried it w/o units and it seemed to work, but I'd like to be able to keep units in there.

It should work with units.

You could have had attached the new file in your response above - choose "Use advanced editor" in th eupper right corner.

While you are sorting out how to attach a file (the forum software used here unfortunately is quite confusing and not user friendly defaulted) I think it dawned to me what the problem could be.

You wrote about two equations in two variables.

If these two varaibles have different units and you try to assign the result of Find to a single variable name you run into troubles, because Mathcad would not allow different units in a vector/matrix.

But there is a way out - see attached.

FindWithUnits.png

And I just tried the vector method you gave me and it worked! Thank you so much! Big credit for you.

Now I'm trying to solve an equation for a variable, and then solve the equation. I'm able to use the symbolic solver to get the equation (for "t" in this case), but then I can't set t= the equation so I can solve for what t actually is. And when i try to use the live symbolics method, it is returning an incorrect answer.

The definition of your constant k1 is wrong. Its so high up you don't see it. Drag it down and see yourself.

Edited: See attached

Ah, right you are! That gave me a correct value for t using that function, but now how do I use t as a variable? When I type t= to display the answer it says the variable is undefined? And also if I solve for t symbolically in the original equation like I did in the worksheet, is there a way to set t= to that equation so that it will solve for t? Sometimes it is nice to see t=(equation) and then t=answer, if you know what I'm saying.

Travis Bailey wrote:

Ah, right you are! That gave me a correct value for t using that function, but now how do I use t as a variable? When I type t= to display the answer it says the variable is undefined? And also if I solve for t symbolically in the original equation like I did in the worksheet, is there a way to set t= to that equation so that it will solve for t? Sometimes it is nice to see t=(equation) and then t=answer, if you know what I'm saying.

Don't think you want t to be set equal to your equation (nevertheless you could do so - see attached). I dont know why you would like to see t=(equation) as t is not an equation, but maybe I am missing the point.

I guessed you simply want to assign the symbolic solution value to a variable. I have done that in the sheet I attached in the last post, but I preferred to name the solution t.1. You may change that to t if you like, but I prefer to distinguish between an independent variable (t) and a specific value (t.1).

If thats not what you are after, post again.

I see. I'n looking at your worksheet, how did you set t2= to the equation and then solve for it? It's interesting how you solved for t1 and t2 two different ways. I have a lot to learn

Travis Bailey wrote:

how did you set t2= to the equation and then solve for it?

Its a nirmal assignment you get by typing ":". If you have already typed the solve part you have to take care that the insertion cursor (the vertical blue line) is on the left (Insrt key switches),

It's interesting how you solved for t1 and t2 two different ways.

If you are speaking of the first set of t1 and t2 - thats your manually solved expression, I simply assigned it a variable.

Thanks. I ended up just copying the equation and then setting t=(paste)

Thanks a lot for all of your help!

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waqas aslam wrote:

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