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StuartBruff23-Emerald V
23-Emerald V
November 21, 2021
Question

How does/should the Is Element Of operator treat NaNs?

  • November 21, 2021
  • 1 reply
  • 2535 views

Whilst playing around with the Is Element Of operator in Mathcad Express 7, I noticed the following:

 

StuartBruff_0-1637522789270.png

 

I was surprised to see that Mathcad thinks that NaN is a Real (and hence Complex), but not an integer.   

 

Is this just a case where one should expect inconsistent results from applying non-NaN-specific functions to a NaN?  If so, I think there should be a warning about this behaviour on the Is Element Of Help page.

 

Or is it something that should be corrected?

 

The red error arises because only the symbolic processor can test for rationals and Mathcad Express doesn't have symbolics.  Consequently, I don't know whether Is Element Of's NaN behaviour extends to symbolics.

 

Stuart

 

I discovered the above whilst trying to write a couple of data type identification functions.

 

2021 11 21 H.png

 

2021 11 21 I.png

 

1 reply

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Werner_E25-Diamond I
25-Diamond I
November 21, 2021

Here is how the symbolic processor treats NaN (done in Prime 6) for your information

Werner_E_0-1637533282542.png

 

    S
    StuartBruff23-Emerald VAuthor
    23-Emerald V
    November 22, 2021
    @Werner_E wrote:

    Here is how the symbolic processor treats NaN (done in Prime 6) for your information

    Werner_E_0-1637533282542.png

     

    The symbolic processor just returns the expression unevaluated?  Strange, I wasn't expecting that.  How does it evaluate integer, rational, real & complex numbers and strings & functions?

     

    Stuart

    W
    Werner_E25-Diamond I
    25-Diamond I
    November 22, 2021
    @StuartBruff wrote:
    The symbolic processor just returns the expression unevaluated?

    Yes, it treats NaN like an unknown variable. There is no difference whether "units/constants in symbolics" is turned on (like in the screenshot) or turned off.

    According to numbers the result is as expected, strings are not seen as numbers as it should be and functions ... see yourself. The function name alone is simplifed to "function", otherwise the function is evaluated and we get a result only if its a constant number

    Werner_E_0-1637544559259.png

    The "assume" modifier is ignored

    Werner_E_1-1637544867660.png

     

     

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