topic Re: Solve x in equation and awsner in mm in Mathcad

Solve x in equation and awsner in mm

AS_10669138 — Fri, 28 Apr 2023 12:37:10 GMT

Re: Solve x in equation and awsner in mm

terryhendicott — Fri, 28 Apr 2023 14:13:59 GMT

Please upload your worksheet rather than just an image

Re: Solve x in equation and awsner in mm

Werner_E — Fri, 28 Apr 2023 19:16:20 GMT

That will end in a polynomial of order 4.

Prime may be able to solve it numerically, but I doubt that you will see a decent symbolic solution.

Obviously you know about symbolic solving with "solve". So you sure already tried that on your equation - what was the result?

Re: Solve x in equation and awsner in mm

AS_10669138 — Tue, 02 May 2023 09:29:08 GMT

when using the symbolic solving function, we get the following answer.

Re: Solve x in equation and awsner in mm

Werner_E — Tue, 02 May 2023 10:57:35 GMT

So it looks you get your answer anyway!? Whats the problem.

Primes symbolic unfortunately does not know anything about units and treats them as unknown variables - hence the ugly result.
Sometimes it helps to turn on the calculation option to use units in the symbolics but it doesn't in case of your example.

Assign the result a variable and evaluate that variable numerically so you get the two result in a more meaningful display and if you are only interested in the positive (larger) result, you can use the "max" function to do the job:.

BTW, the "solve" above the shown region fails because the variable to solve for already was assigned a value. You can use "clear([variable name])" or "clear.sym([variable name])" to be able to use that variable name for solving.

As you are not looking for a symbolic result but rather a simple numeric one, you may also consider not to use the symbolics but rather numeric methods (either a solve block or the "root" function).

The precision of the result is dependent on the setting of the system variable TOL. Its default value is 10^-3. I set it to 10^-6 to get the same three decimals as with the symbolic solve. You may set the value for TOL either somewhere at the stop of the sheet or with the ribbon menu (Calculation - Worksheet Settings),

Worksheet in format P9 attached

Re: Solve x in equation and awsner in mm

Werner_E — Tue, 02 May 2023 11:08:11 GMT

Addendum:

Using clear() or clear.sys() does not work in your example! Prime does not like the name of the variable you are looking for.

This sure is a bug in Prime and you may consider reporting it to PTC support if you like.

When I replace your variable "x" for an "X", the same problem arises - the symbolic result is different, it uses a branch (if) and an auxiliary variable "_c" is popping up in the solution. This sure should not happen.

using solve variable "x":

using solve variable "X":

Prime still seems to be quite buggy (especially the symbolics)!

Using "substitute" could be a suitable workaround to avoid having to duplicate the equation. You still have to use clear() or clear.sym()

Re: Solve x in equation and awsner in mm

LucMeekes — Tue, 02 May 2023 21:23:03 GMT

At the top of your sheet, before anything else, define:

Then, at the position of equation (7), you can:

and if you only want the (most) positive result:

Success!
Luc

Re: Solve x in equation and awsner in mm

AS_10669138 — Wed, 03 May 2023 14:29:06 GMT

Thank you very much for your answer, i realised that one formula was incorrect (q*l^4/384EI) should be (5*q*l^4/384EI) and when i changed this i couldnt get an answer out of your formula.

im also realised that i am are more interested in getting a symbolic result for the efficient width b´LVL than the exact value in mm.

would it be possible to get a symbolic result for the unknown variable b´LVL ?where b´LVL is alone on one side and removed from the other. i am not so good with mathematic equations so if you could solve this problem for me it would be really helpful!

Re: Solve x in equation and awsner in mm

LucMeekes — Wed, 03 May 2023 15:03:42 GMT

See attachment.

Success!
Luc