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A
akrisciunas1-Visitor
1-Visitor
April 10, 2010
Question

Difficulty Rearranging Equation

  • April 10, 2010
  • 4 replies
  • 10078 views
Hello there,

I'm an engineer by trade and am doing a bit of light theoretical work. I have limited experience using MathCAD for anything other than basic calculation sheets.

I have two equations that I've defined symbolically, and I have defined all variables and Boolean relationship. I'm attempting to use the "given": ___ "find":____ functions but am not having much success.

Attached is the sheet I'm using. Essentially I've defined CrA and CrB algebraically. I would like to solve for "L" symbolically such that CrA=CrB.

Intuitively I feel that mathcad should be able to crunch out some sort of relationship that I can later simplify.

Any suggestions from the more experienced users would be greatly appreciated!

Thanks,
Andrew

4 replies

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
April 11, 2010
We must use not := but = (boolean equal) operator after the Given key word!

Val
http://twt.mpei.ac.ru/ochkov/v_ochkov.htm
A
akrisciunas1-VisitorAuthor
1-Visitor
April 12, 2010
Thanks for the replies guys. Still having difficulty. I managed to simplify the equation I want to rearrange - see jpeg.

I plotted both functions using dummy values and they do indeed intersect, so I'm unsure why MathCAD cannot find a solution.

See attached jpegs
P
ptc-13682881-Visitor
1-Visitor
April 12, 2010
On 4/12/2010 12:56:51 AM, akrisciunas wrote:
>Thanks for the replies guys.
>Still having difficulty. I
>managed to simplify the
>equation I want to rearrange -
>see jpeg.
>
>I plotted both functions using
>dummy values and they do
>indeed intersect, so I'm
>unsure why MathCAD cannot find
>a solution.
>
>See attached jpegs
_______________________________

You have red and no error message ?
Keep reducing at least up the point I did and see that there is nothing to solve except for b = 0.

jmG



P
ptc-13682881-Visitor
1-Visitor
April 11, 2010
Anything useful in there ?
in Mathcad 11 that you should read .
If you get the error message "singular matrix",
uncheck the box in the work sheet options
"Use strict singularity checking for matrices".


jmG
P
ptc-13682881-Visitor
1-Visitor
April 13, 2010
On 4/10/2010 3:38:07 PM, akrisciunas wrote:
...
>I have two equations ...
==> then you said "I WOULD LIKE TO SOLVE FOR L HERE:"
==> "If L is L then there are two solutions"
==> Then go to the next steps of your project ?


>Thanks,
>Andrew



L
LouP12-Amethyst
12-Amethyst
April 13, 2010
My own experience is that the symbolic processor often doesn't find relatively simple solutions that can be found manually, and sometimes it can.

this is a case where a symbolic soltion is relatively simple, but the myriad definitions add a lot of hair which can hide the underlying relations. The attached file sshows hand-holding of the symbolic proc. with all the constants simplified as much as possible.

This is a human guided sol'n with the symb. proc used for most of the manipulations/evals.

Lou
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