Difficulty Rearranging Equation

[akrisciunas]

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

[ptc-1368288]

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

[ValeryOchkov]

We must use not := but = (boolean equal) operator after the Given key word!

Val
http://twt.mpei.ac.ru/ochkov/v_ochkov.htm

[akrisciunas]

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

[ptc-1368288]

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

[TomGutman]

With those horrendous exponents? You have shown the existance of a solution, and I'm sure the Mathcad numeric processor can find that. But that is very different from any general symbolic solution.
__________________
� � � � Tom Gutman

[ptc-1368288]

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
_______________________________

With those horrendous values, you have managed to cross the two functions, on the independent variable 'L'. Their crossing point is the numeric root function about 'L'.

jmG

[RichardJ]

On 4/12/2010 12:56:51 AM, akrisciunas wrote:

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

Not every problem has a symbolic solution. Even if it does, there is no guarantee that a symbolic math engine can find it, and even if it can it may be so huge and unwieldy as to be effectively useless. If you just want to find the intersection then solve the problem numerically. Assign values for all the variables, give a guess value for L, and then numerically evaluate the Find at the end of the solve block.


Richard

[AlvaroDíaz]

Providing numerical values for the unknows we can show how to solve numerically your equation, but what I can't understand is the sintaxis for tcor := t - t C. What is it?

Regards. Alvaro.

[ptc-1368288]

On 4/12/2010 5:57:48 PM, adiaz wrote:
...
:= t - t C. What is it?
>
>Regards. Alvaro.
________________________

Nothing by itself
something in context(t-C*t)/ ...t
result is (1-C)/
Go back to my demo image.

jmG

[LouP]

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

[ptc-1368288]

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