Solving an equation symbolically

[ptc-6670542]

Just started using MathCAD today, so I am very new to it. I am basically trying to solve a complicated equation (shaft diameter sizing) with a bunch of known variables in terms of 1 unknown variable. I want to have the answer in symbolic terms so I can use the same equation for different sized shaft calculations. How the heck do I do this? I have been looking at the help files and other posts for some time now and still am not any clearer. Please see the attached file for reference.

Thanks in advance!

Rob

[Fred_Kohlhepp]

You need to write your functions in terms of the variable so that they compute.

For multiple uses you can employ a "solve block" as a function; Mathcad will find the values that fit.

Attached is a "one of" solution for your problem as posed. Adding the solve block is left as an exercise . . .!

[ptc-6670542]

Thanks for the response, but not exactly what I am needing. I really need to have the equation solved for Te symbolically. Is there a way to do that, rather than just get a numerical answer?

[Werner_E]

Thanks for the response, but not exactly what I am needing. I really need to have the equation solved for Te symbolically.

Why? In you first posting you wrote

"I want to have the answer in symbolic terms so I can use the same equation for different sized shaft calculations."

If thats your motivation, then no symbolic solution would be necessary.

[ptc-6670542]

My end goal is to be able to put this in a user-friendly excel sheet for others to use for future calculations. We don't have a sitewide license for MathCAD, so doing the calculations in there would mean spending hours of my time on calculations for new designs. If I have a function for Te is terms of the known variables, I can just plug this into excel. Then the other users can change the applicable variables for their specific designs.

[Werner_E]

And the symbolic solution has to be dependend on all 15 symbolic variables?

[ptc-6670542]

Ideally yes, I want to leave the solution as general as possible to allow for a wider range of use.

I combined some variables to condense the equation in the hope that I would get a solution, and I am getting an error now that says "symbolic result too large to display." So at least it is solving the equation. Is there a way to force an output? Again I don't want to be forced to evaluate it in MathCAD if at all possible.

[Werner_E]

Robin DeJager wrote:

Ideally yes, I want to leave the solution as general as possible to allow for a wider range of use.

Then I think Mathcad Prime will not be the tool to use.

I combined some variables to condense the equation in the hope that I would get a solution, and I am getting an error now that says "symbolic result too large to display."

Did you try the symbolic solution after you defined your various variables? Then the symbolics would use those values and not general variables.

I tried before the variable definition and only got a solution after I got rid of the cubic root and solve the equation ....=D^3

The solution is a matrix with 1 column and 2 rows and is, according to Prime, too large to display but can be used in subsequent calculations if assigned to a variable or function. I tried both to no avail, so it seems to be a bug.

But that doesn't matter for your purpose as you need to see theresult. I guess, no matter what tool you would use to get your result, it would be too large and unhandy to implement in Excel anyway. So why don't you implement the whole calculation in Excel from the very beginning and get the value for Te using Excel's solver?

[ptc-6670542]

I was going the same route as you, solving with general variables. I also had to get rid of the cubic root. I will explore defining the variables, then trying to solve.

I have been exploring the excel solver option simultaneously as well. I think I am rather close there, however there are still some manual steps to perform as excel doesn't like symbolic equations. At least not that I am familiar with.

Thanks for your help on this.