Problem with this equation solving on Mathcad Prime 9

[DR_7356149]

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.

[Werner_E]

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.

[DR_7356149]

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.

[Werner_E · Accepted solution]

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.

[DR_7356149]

I'm extremely grateful for the information, very valuable to me. I greatly appreciate your time and knowledge. You are a kind genius.

If I have any questions about the document you sent me, I'll write to you. I'm reviewing it in detail.

[Cornel]

Do you have any example showing the effect of having checked/unchecked this option of "Units/Constants in Symbolics" in the calculation options? I had enabled this in the past at some moment due to curiosity, but I was not able to spot the difference  and when it's good to have checked this option in the calculations.

[Werner_E]

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@Cornel wrote:

Do you have any example showing the effect of having checked/unchecked this option of "Units/Constants in Symbolics" in the calculation options? I had enabled this in the past at some moment due to curiosity, but I was not able to spot the difference  and when it's good to have checked this option in the calculations.

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Option "Units/Constants in Symbolics" is UNchecked:

Here the same calculation with the option checked.
You must recalculate the sheet (F9 or F5) to see the effect after changing the option.

Unfortunately checking this option does NOT mean that the symbolics would be unit-aware and know that Volt divided by Ampère is Ohm. The symbolics is still dumb in this respect but at least the labels used when defining the variables are correctly applied and so the symbolic result can be evaluated numerically.

I am not sure why this option isn't checked by default or why we have that option at all. I can't see where it would be beneficial to uncheck it.

[Cornel]

Ok, i see now. I can agree then that it's better to have this option checked.

[Cornel]

 I said above statement within it's symbolic  unit-aware limitation. Indeed it would have been much more beneficial if also the symbolics would be unit-aware.