Re: Re: variable "K"? (Really strange behavior . . . )

*To*: mathgroup at smc.vnet.net*Subject*: [mg69210] Re: [mg69182] Re: variable "K"? (Really strange behavior . . . )*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Fri, 1 Sep 2006 18:41:20 -0400 (EDT)*References*: <ed6918$jho$1@smc.vnet.net> <200609011041.GAA25571@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

They probably didn't protect K because it is usually only associated with some type of automatic output - such as an integration dummy variable. Even then, it usually appears in a unique form like K$12312. I think it would be okay for you to assign K a value if you wanted to. On 9/1/06, AES <siegman at stanford.edu> wrote: > Final comments (my final comments, anyway) on the "strange behavior of > K" observation I posted: > > 1) The explanation clearly lies in the two responses appended below > (and thanks). > > 2) Some further exploration on my part seems to show that the 7 single > capital letters C D E I K N O all have (at present, anyway) one > or another form of special "system" meaning in Mathematica. Six of > these 7 letters (all but K) also share the properties that they > > (a) Have an entry in the online Help system, and > > (b) Issue a "Protected" warning if you try to use them as symbols. > > Unfortunately, K has neither of these attributes, which makes it much > less apparent to non-experts that using it as a symbol name will cause > bizarre difficulties -- especially since all the other 19 single > capitals can apparently be used as symbols without trouble. > > 3) It might might be nice if Wolfram would Protect and/or include in > the online Help system *all* the special symbols in the entire system. > But, this may be difficult technically (?), and leaves open the chance > for some of these special symbols to get inadvertently omitted. > > So, despite the attractions of writing an optics notebook using the > standard notation of "a" for radius of a circular fiber, "v" for its > fiber v parameter, "A" for its cross sectional area, "V" for its volume, > and "K" as the standard notation for the thermal conductivity of glass, > I guess the safest course is for the user to conform to the computer, > and never use a capital letter as the initial letter of a symbol. > > ===================================================== > Notice the usage message for K. This is because K is a System symbol: > > In[2]:= Context[K] > > Out[2]= System` > > Carl Woll > Wolfram Research > ===================================================== > The answer seems to be that K's Context is System, not Global, and unlike > many System symbols it is not Protected, which is why it could be set to > 0.6. In fact, of the 1984 symbols in System (in version 5.2) 515 are not > protected, and K is one of those: > Length[Select[Names["System`*"], FreeQ[Attributes[#], Protected] &]] > Luckily, things like Pi, E and I are protected! > > Dr A.H. Harker > Department of Physics and Astronomy > University College London > ===================================================== > > -- http://chris.chiasson.name/

**References**:**Re: variable "K"? (Really strange behavior . . . )***From:*AES <siegman@stanford.edu>