topic Re: Derivative problem in Mathcad

Derivative problem

vladstavar — Sat, 02 May 2020 17:51:32 GMT

I used the derivative function but now i need to find L how to do it ?

Re: Derivative problem

terryhendicott — Sun, 03 May 2020 00:14:45 GMT

You need to define values for "U", "R", & "L"

Cheers

Terry

Re: Derivative problem

Werner_E — Sun, 03 May 2020 01:03:53 GMT

You equation can't be solve by elementary means, so Prime can't find a symbolic solution.

But if you provide values for U, R and t you can get a numerical solution for L:

This is probably not the solution you are looking for, but when forced to switch into float mode, the symbolic will only return one solution with no control over it.

Note that I used the prime operator for the derivative.

Another way would be to use the usual derivative operator as you did and assign the result to a new function (I called it "f1" in the pic below and made it dependent on t AND L).
You may add units and use the numeric "root" command instead of the symbolic solve. Numerical methods like "root" or a solve block a native to Prime and can handle units (the symbolics doesn't know anything about units):

Prime 6 worksheet attached

Re: Derivative problem

LucMeekes — Sun, 03 May 2020 17:54:26 GMT

"You equation can't be solve by elementary means, so Prime can't find a symbolic solution."

Stupid Prime.

Success!

Luc

Re: Derivative problem

Werner_E — Mon, 04 May 2020 04:00:59 GMT

@LucMeekes wrote:

"You equation can't be solve by elementary means, so Prime can't find a symbolic solution."

Stupid Prime.

LambertW is not "elementary" and can usually only be evaluated numerically

But I second your "Stupid Prime" nonetheless for many other reasons 😉