# Re: Strange behavior of logical variable to not operator

From: David Brown <dbrown_at_nyahnyahspammersnyahnyah>
Date: Tue Mar 01 2011 - 18:10:30 MST

Hi Gibies,

There is a problem here and thank you for pointing it out. However, it is not what it might seem at first glance. There is one issue, admittedly somewhat serious: the conversion of the default logical missing value to a string is not working correctly. When you call 'print' with your variable 'full' set to the default missing value, "Missing", as follows:

print("full = " + full)

the value of 'full' gets converted to a string -- incorrectly, it turns out. However, the variable 'full' still has the correct value and the .not. operator is working correctly. You can see this if you print the variable and the expression without converting them to a string. If the first part of your code is changed from:

print("A1 : Defineing full = new(1,logical)")
full = new(1,logical)

print("full = "+full)
print(".not.full = "+.not.full)

to

print("A1 : Defining full = new(1,logical)")
full = new(1,logical)

print(full)
print(.not.full)

Instead of your output below you get:

(0) A1 : Defining full = new(1,logical)

Variable: full
Type: logical
Total Size: 4 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
Number Of Attributes: 1
_FillValue : Missing
(0) Missing
(0) Missing

which is correct based on the rule that any operation applied to a missing value yields a missing value.

Setting the missing value to True, as you do in case B, inevitably leads to results that seem weird, even though all the results in your B scenario are correct by the rule above. Likewise with scenario C where the missing value is set to False. In most cases, although allowed, it is not advisable to change the missing value of logical variables from the default. Case D is the same as A and has the same error. Thanks much for pointing this out. I'm not sure how this has managed to slip by for such a long time. But it will have a high priority for getting fixed quickly.
-dave

On Mar 1, 2011, at 9:34 AM, gibies george wrote:

> Here I have analysed 12 different cases of logical variable find its behavior to not operator.
>
> My script is attached
>
> The output is as follows.
>
> Please note the potions with red font colour.
>
> I am using NCAR Command Language Version 5.1.1 on Fedora 11 operating system
>
> (0) A1 : Defineing full = new(1,logical)
> (0) full = True
> (0) .not.full = True
> (0) case A2 : full = True
> (0) full = True
> (0) .not.full = False
> (0) case A3 : full = False
> (0) full = False
> (0) .not.full = True
> (0) B1 : Defineing full = new(1,logical,True)
> (0) full = True
> (0) .not.full = True
> (0) case B2 : full = True
> (0) full = True
> (0) .not.full = True
> (0) case B3 : full = False
> (0) full = False
> (0) .not.full = True
> (0) C1 : Defineing full = new(1,logical,False)
> (0) full = False
> (0) .not.full = False
> (0) case C2 : full = True
> (0) full = True
> (0) .not.full = False
> (0) case C3 : full = False
> (0) full = False
> (0) .not.full = False
> (0) D1 : Defineing full = new(1,logical)
> (0) full = True
> (0) .not.full = True
> (0) case D2 : full = True
> (0) full = True
> (0) .not.full = False
> (0) case D3 : full = False
> (0) full = False
> (0) .not.full = True
>
>
> --
> Gibies George, CSIR-RF,
> Climate and Global Modelling Division,
> Indian Institute of Tropical Meteorology,
> Dr. Homi Bhabha Road,
> NCL (P. O.), Pashan,
> Pune 411008, India.
>
> http://sites.google.com/site/gibiesge/
>
> Please Think about the environment. Save paper; Save Trees; and don't print this e-mail unless it is necessary.
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Received on Tue Mar 1 18:10:36 2011

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