Re: Re: confused about == vs === in this equality
- To: mathgroup at smc.vnet.net
- Subject: [mg103777] Re: [mg103750] Re: [mg103732] confused about == vs === in this equality
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Mon, 5 Oct 2009 13:17:29 -0400 (EDT)
- References: <20091003104738.LCJ3I.416659.imail@eastrmwml34> <200910051136.HAA28533@smc.vnet.net>
On 5 Oct 2009, at 20:36, danl at wolfram.com wrote: > he decision, which I believe only goes back a few versions, was to > also > treat infinities in that way. From a mathematical point of view this > makes > sense, and it may well be useful in the innards of some Limit code in > avoiding what would be incorrect cancellations. (Though I have > worked on > that code, I do not recall all specifics, but I think we always > carefully > guarded against this.) This does not seem to be quite true, at least not for all infinities. Infinity == Infinity True I think this is reasonable as in a certain sense there is "only one" positive real infinity. Similarly: DirectedInfinity[I] == DirectedInfinity[I] True and so on. So, I think, as I wrote in my other message in this thread, it is probably the case that DirectiedInfinity[] and Indeterminate are the only symbols with this property. I completely agree with the behaviour of Indeterminate but still have some doubts about DirectedInfinity[] and would like to see an example where having equality return true would cause some sort of problem or weirdness. Andrzej Kozlowski
- References:
- Re: confused about == vs === in this equality
- From: danl@wolfram.com
- Re: confused about == vs === in this equality