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M
Manfred_F12-Amethyst
12-Amethyst
August 8, 2023
Question

Usage of NaN in calculations

  • August 8, 2023
  • 3 replies
  • 3068 views

Every function, which is called with an argument of NaN should deliver NaN as a result !

Some functions deliver odd values such as log, ln, or ln0. Very problematic are the functions min and max which deliver min(NaN)=0 and max(NaN)=0. This can lead to incorrect results, as it was the case in our calculations. This error occured with Prime 8.

Prime8_minmaxNaN.gif

 

 

3 replies

ttokoro
ttokoro21-Topaz I
21-Topaz I
August 8, 2023

Prime 9 also.

image.pngimage.png

So, we should do.

image.pngimage.pngimage.pngimage.png

But, if image.pngthen alsoimage.png

t.t.
W
Werner_E25-Diamond I
25-Diamond I
August 9, 2023
@ttokoro wrote:

 

So, we should do.

image.pngimage.pngimage.png

 

This does not help much as it still fails if NaN is the first entry of the vector!

Werner_E_0-1691572521372.png

 

 

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    August 8, 2023

    Sorry to say, but this is behaviour as designed; according to the Help information on NaN in "About the NaN (Not a Number) Built-In Constant":

    "... A NaN can only be processed by functions specifically written to use it. Other functions may return errors or incorrect results if passed a NaN."

    After all, it's PTC sofware.

     

    Mathcad 11 gives:

    LucMeekes_0-1691527236336.png

    Success!
    Luc

    M
    Manfred_F12-AmethystAuthor
    12-Amethyst
    August 9, 2023

    Hi Luc,

    did you try this on Prime8:

    Prime8_logNaN.gif

    Manfred

    W
    Werner_E25-Diamond I
    25-Diamond I
    August 9, 2023

    The bug (or unexpected and undesired result, as its behavior according to the help) with "min" and "max" is already present in Mathcad, so we can blame PTC only for not fixing it.

    Werner_E_1-1691572974962.png

    What we can blame PTC for is for making it even worse as your example with the logs showed

    Werner_E_2-1691573066793.png

    I am surprised that the imaginary part is pi. Would expect at least an integer multiple of 2 pi !?

    Here is the same in MC15

    Werner_E_3-1691573100074.png

    Here is something "nice", too

    Werner_E_4-1691573625027.png

    Note that NaNi and also the number in the exponent are labeled as "Unit" ????

    In MC15 this still was OK

    Werner_E_5-1691573703956.png

     

    Even though the help states that using functions on NaN may give wrong results, you may consider opening a ticket at PTC support and report this bug and/or demand that this undesirable behavior should be changed.

     

     

    ttokoro
    ttokoro21-Topaz I
    21-Topaz I
    August 9, 2023

    Using vector M, Edit: Without NaN fix.

    image.pngimage.pngimage.png

    image.pngimage.pngimage.png

    t.t.
    W
    Werner_E25-Diamond I
    25-Diamond I
    August 9, 2023

    Which results do you get when you use a vector without any NaN's? 😉

     

    EDIT: AH, I see that you have editted your post and fixed your functions to deal correctly with that case 😄 

      M
      Manfred_F12-AmethystAuthor
      12-Amethyst
      August 9, 2023

      I would expect that min() or max() filters out the NaN and calculates then min/max from the rest. If there is no value left (all values are NaN) then the result should be NaN. I tried several combinations and it seems to depend on the sign and position of NaNs:

      Prime8_minmaxNaN2.gif

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