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J
JBlackhole16-Pearl
16-Pearl
April 9, 2020
Solved

Discretize a continuous function to get its max value?

  • April 9, 2020
  • 3 replies
  • 1984 views

I can't remember hence the silly question. If one has a continuous function (in my case of time) and one wants to only return the max (absolute) value of the function (range 0..tend), does one needs to discretize the function?

a example

y(t):t^2  wit t = 0..5

max(y(t)) does not return 25

Best answer by AlanStevens

Make sure t is a vector not a range variable:

 

max.JPG

Alan

 

3 replies

S
StuartBruff23-Emerald V
23-Emerald V
April 9, 2020

I don't think you do if you've got Premium Prime (ie, not Express).  You can use a solve block or maximize function, as described in:

 

https://support.ptc.com/help/mathcad/r6.0/en/index.html#page/PTC_Mathcad_Help%2Fabout_solve_block_functions.html%23wwID0EYDC5

 

https://support.ptc.com/help/mathcad/r6.0/en/index.html#page/PTC_Mathcad_Help%2Fexample_optimizing_a_function.html%23wwID0E4EJJB

 

If it's an analytic function, then you could also either try using symbolic differentiation to find the maximum (1st and 2nd derivatives)

 

Stuart 

    A
    AlanStevens19-TanzaniteAnswer
    19-Tanzanite
    April 9, 2020

    Make sure t is a vector not a range variable:

     

    max.JPG

    Alan

     

      S
      StuartBruff23-Emerald V
      23-Emerald V
      April 9, 2020

      You need to be careful how many points you evaluate a function over when looking for its maximum within a given range.

       

      If you don't have enough points, you will not likely get the prize of picking the right maximum or even seeing most of them.

       

      Here's the difference between 0..5 and 0,0.01..5.  Quite different beasts.

       

      2020 04 09 A.png

       

      2020 04 09 B.png

       

      Stuart

        J
        JBlackhole16-PearlAuthor
        16-Pearl
        April 9, 2020

         Thanks for the info. 

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