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DR_73561493-Newcomer
3-Newcomer
June 1, 2024
Solved

Problem with this equation solving on Mathcad Prime 9

  • June 1, 2024
  • 1 reply
  • 2115 views

Hi everyone,

 

I solved for the variable Fthrusters in the equation WE:


The solution shows:
1° term unit: m.kg/s^2 = N
2° term unit: N.s^2/s^2 = N


Why does the solution choose to keep them as independent terms if they can be operated?
Even changing the units of the previous variables from N to kg.m/s^2, the 'supposed' solution remains unresolved.

Thank you.

Captura de pantalla 2024-06-01 170251.png

Best answer by Werner_E

No! I was not suggesting doing a unit-less calculation as in your Case 2.
What I was suggesting was to assign the symbolic result to a variable (F := WE ->(solve)....) and then evaluate that variable numerically (using the normal equal sign, F = ....).

As an alternative I suggested using pure numerical methods instead of using the symbolics.

And I sure won't suggest solving the equation 'manually' and use the derived result as in your Case 3.

 

Find a couple of suggestions, ideas and comments in the attached Prime 9 file.

If you have any additional questions, feel free to come back and ask.

 

 

1 reply

W
Werner_E25-Diamond I
25-Diamond I
June 1, 2024

The symbolics does not know anything about units and treats them as unknown variables. Thats the reason you don't get a simplified result.

You may assign the calculation to a variable and if you evaluate this variable numerically you should see the result you expected (you should check the option "Units/Constants in Symbolics" in the calculation options).

 

As you are just looking for a numeric result, you may consider to just use numeric methods. Prime offers either a solve block with "find" or the "root" function. Look them up in the help.

 

For further help you would have to attach your worksheet, not just posting a picture.

    D
    DR_73561493-NewcomerAuthor
    3-Newcomer
    June 2, 2024

    Thank you @Werner_E . I will check the "find" and "root" functions.

    I attached the file below:

    Case 1: It's ideal because it allows me to input the equations formally and expect Mathcad to solve for the variable.

    Case 2: If I understood correctly, this is what you're suggesting; using numerical variables without units.

    Case 3: That's what I'm currently doing, which is finding the variable directly by rearranging the equation. But it's not practical to do this with every equation.

    W
    Werner_E25-Diamond IAnswer
    25-Diamond I
    June 2, 2024

    No! I was not suggesting doing a unit-less calculation as in your Case 2.
    What I was suggesting was to assign the symbolic result to a variable (F := WE ->(solve)....) and then evaluate that variable numerically (using the normal equal sign, F = ....).

    As an alternative I suggested using pure numerical methods instead of using the symbolics.

    And I sure won't suggest solving the equation 'manually' and use the derived result as in your Case 3.

     

    Find a couple of suggestions, ideas and comments in the attached Prime 9 file.

    If you have any additional questions, feel free to come back and ask.

     

     

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