There is no keyword named [_], Solving unknown variable

[MelB]

See snip below & attached. I'm trying to solve for z_pna, such that the sum of the tension forces equals the sum of the compression forces.

[LucMeekes · Accepted solution]

The variable you want to solve for needs to be part of the equation. That is not the case above. You should have z_pna be a parameter to both  SigmaT and SigmaC. This in turn means that also Tsr and Csrw must be functions, with z_pna as a parameter.

Considering that all other items are numerically defined, there's no need to try to solve this symbolically (which you do when you use that arrow). Better try a numerical solver, such as the root() function.

And when you really do want to use the symbolic solver:

1. You need to use the 'solve' keyword.

2. You should consider that the symbolic processor does not know about units by default, and while there is a setting to let it take account of them, sometimes it simply doesn't work.

Success!

Luc

[Werner_E]

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@LucMeekes wrote:

2. You should consider that the symbolic processor does not know about units by default, and while there is a setting to let it take account of them, sometimes it simply doesn't work.

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How true! In case of this example it works OK,  though. You might have to recalculate the sheet once or twice.

But I fully agree that if just a numeric result is looked for, a numeric method like a solve block or the root function should be used, rather than the unit-unaware symbolic "solve".