# Re: [R] Sweave and complex numbers

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Mon 11 Jul 2005 - 23:04:52 EST

Duncan Murdoch <murdoch@stats.uwo.ca> writes:

> > Question: why does \verb=c(1,1+1i)= get printed as
> > \verb=c(1,1 + (0+1i))= ?
>
> The R parser only understands pure imaginary constants as complex
> numbers. It parses 1+1i as the sum of the real constant 1 and the
> complex constant 0+1i.
>
> This isn't easy to work around. Sweave could special case these, or the
> parser or deparser could, but it looks messy to me. I'd guess the best
> solution would be if it happened in the parser (i.e. a real constant
> plus an imaginary constant was folded into a complex constant), but
> right now our parser doesn't do any sorts of optimizations like this.
> It's not easy to add the first one, not least because the parser doesn't
> know for sure that 1+1i really is a complex number: you might have
> redefined the meaning of "+".

Hmmmm... I'd say that the user would deserve what she gets in that case. I suspect that the real issue is that R's tokenizer is hand-written and not smart enough to recognize complex constants. Figuring out whether there is a good reason for that or whether we might actually use an automatic tokenizer like flex is somewhere on the far end of my want-to-do list...

One thing that could be done quite immediately is to let the deparser forget about a zero real part and drop the parentheses in that case. After all "1i" is perfectly legal R, and

> identical(1i,0+1i)

[1] TRUE (Those parse/deparse asymmetries are maddening. *Next* time we redesign R we should get this straightened out....)

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Received on Mon Jul 11 23:20:30 2005

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