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-MFra-21-Topaz II
21-Topaz II
September 18, 2024
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Searching a symbolic element in a square matrix (Using MATHCAD 15)

  • September 18, 2024
  • 2 replies
  • 2003 views

A big hello to everyone here,

I'm looking for a little program that receives as parameters only a square matrix of alphanumeric elements and a symbolic element to search in it. The program must return the row and column indices of the element searched. Is anyone able to make it? It seems simple to me. I thank very much whoever wants to do it.

Best answer by Werner_E

The numerics can not distinguish between -L.0*s and -0.000005

So a numerically evaluated "match" command will give you the position of both and also, depending on the setting of the system variable TOL even others which are "close" enough.

A symbolically evaluated "match" will give you the result you probably are looking for.

Werner_E_2-1726670642542.png

 

Werner_E_3-1726670950307.png

 

And, no, you can't look for just L.0, you have to use the full exact expression.

 

 

 

2 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
September 18, 2024

That's quite the challenge:

LucMeekes_0-1726669400087.png

The 'item'

LucMeekes_1-1726669439915.png

does not occur (as an element) in the matrix, in contrast to

LucMeekes_2-1726669515422.png

Luc

    W
    Werner_E25-Diamond IAnswer
    25-Diamond I
    September 18, 2024

    The numerics can not distinguish between -L.0*s and -0.000005

    So a numerically evaluated "match" command will give you the position of both and also, depending on the setting of the system variable TOL even others which are "close" enough.

    A symbolically evaluated "match" will give you the result you probably are looking for.

    Werner_E_2-1726670642542.png

     

    Werner_E_3-1726670950307.png

     

    And, no, you can't look for just L.0, you have to use the full exact expression.

     

     

     

      S
      StuartBruff23-Emerald V
      23-Emerald V
      September 18, 2024

      Argh, me hearty! I'm in full on pirate mode, today, and 'tis capturing your worksheet I being!

       

      A random thought was making its merry way through the aether and got tangled up in my skull.  Poor thing.  However, whilst it was there it wondered what would happen if I looked for coefficients of the desired variable.  Sooo, ....

       

      2024 09 18 B.png

       

      2024 09 18 C.png

       

      Stuart

        W
        Werner_E25-Diamond I
        25-Diamond I
        September 18, 2024

        Congratulations on your pirate genes and the 'random thought' in your head. That really is a very clever approach!

        Due to the nature of "coeffs" it will work pretty well as long as the variable is in a polynomial term. It will not find the position if its inside a function like sin or exp as then coeffs returns just a 1x1 matrix.
        maybe if we combine it with "series" ....

        Werner_E_0-1726688833331.png

        It fails if L.0^2 is replaced by L.0^3 because of the modifier "3" in "coeffs".

         

        I also came across an effect with "coeffs" which I was not aware of and which puzzled me at first - I seem to have completely forgotten about the additional "degree" modifier 🙂

        Werner_E_3-1726689348001.png

         

         

         

         

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