assume' not working with find(x,y,z) ...?

[SylvainFlamant]

I was solving a simple geometry problem for my son... I reduced the problem to a set of 3 equations with 3 positive unknown variables ( 3 distances so they need to be positive) .

Using the symbolic engine, Mathcad 14.0 has no problem finding a set of 4 solutions... including the one I was looking for , with positive numbers.

So I wanted to add the constraint that the solution had to be real and positive using the modifier "assume, ALL = RealRange(0,100))" in conjunction with the Given and Find(a,b.c) block.

I know that the syntax "assume, ALL = RealRange(0,100))" works when trying to simplify one single equation with multiple variables as shown in the tutorials, but it seems to be ignored in the context of a Given and Find block...

Maybe somebody can tell me what I am doing wrong in the attached file.

Thanks

sylvain flamant

[AlvaroDíaz]

Writing in french, but the 1st edition appear in spanish, by Milan Kundera, Czech writer:



Alvaro.

[ptc-1368288]

On 3/3/2009 3:05:36 PM, sflamant wrote:
>I was solving a simple
>geometry problem for my son...
>I reduced the problem to a set
>of 3 equations with 3 positive
>unknown variables ( 3
>distances so they need to be
>positive) .
>...
>sylvain flamant
______________________________

The proposal is based on my previous advices:

1. Get the raw simplest symbolic solution.
2. Collect the numerical solution.
3. Apply a more generalized "mask extractor".

Note that the "mask extractor" can be user defined to suit other task for more general applications and where specific type of values are wanted. My point here is again the reverse engineer method from what you don't know in advance. This way the entire procedure is traceable by isolation and by same token traceable to the symbolic that you can cross check with other symbolic engines, even back to paper-pencil.

A while ago (years), very similar "mask extractors" have been used for special project in this collaboratory. This one here is a nuanced and specific version from a family of masked extractors.



jmG

[ptc-1368288]

... a much different, but "mask-solve-extract"

jmG

[SylvainFlamant]

Thank you Jean,

This is an interesting "trick".

sylvain flamant

[ptc-1368288]

On 3/16/2009 12:54:04 PM, sflamant wrote:
>Thank you Jean,
>
>This is an interesting
>"trick".
>
>sylvain flamant
________________________

The Mathcad vectorize logical test is extremely powerful. Your example is simple but you can figure switching solutions by masking where the mask may be a logical resulting conclusion for switching from solution to solution in more complex problems, i.e: in real applications.

Welcome, Jean