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V
ValeryOchkov24-Ruby IV
24-Ruby IV
February 4, 2018
Question

Minimize or MinErr

  • February 4, 2018
  • 2 replies
  • 4012 views

I would like to solve this problem

https://community.ptc.com/t5/PTC-Mathcad-Questions/Chebyshev-step-macine-optimization/m-p/500155

not with the Minimize function but with the MinErr function.

But do not know how.

Help me please!

The Mathcad 15 and Prime 4 files are in attach.

2 replies

W
Werner_E25-Diamond I
25-Diamond I
February 4, 2018

Whats wrong with minimize?

Anyway, here is the simplest way of doing it with minerr (you'll have to chose Quasi-Newton as algorithm to get the very same results as with minimze):

Bild.PNG

BTW, it looks like you are using a 4K display like me. Pictures you grab from hat screen are far to large to be inserted here, making the threads hard to read. You should either resize the pics before posting or choose "medium" as size when you insert them in a thread.

W
Werner_E25-Diamond I
25-Diamond I
February 4, 2018

Just gave it a try in Prime4

You have no choice of algorithm

Calculation with minerr takes "endless" time

Result is not as good as the one derived with minimize

 

Facit: Avoid using Prime whenever possible (and its always possible to avoid).

 

Bild2.PNG

V
ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
February 4, 2018

Thanks, Werner!

But I think about this method

MinErrTcheb.png

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
February 5, 2018

minimizeminimizeminerrminerr

V
ValeryOchkov24-Ruby IVAuthor
24-Ruby IV
February 5, 2018

S=?

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
February 5, 2018

You defined S as the error function, so minimizing it gave your answers.

 

Find and Minerr act to satisfy constraints, so finding the minimum error for y(...) = h has the same effect.

 

Note that Minerr is basically Find where Find can't arrive at an acceptable solution.  It's always wise to find out how bad your "minimum error" is, it can be quite unacceptable.

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