From murdoch.duncan at gmail.com  Fri Jul 30 12:13:26 2010
From: murdoch.duncan at gmail.com (Duncan Murdoch)
Date: Fri, 30 Jul 2010 06:13:26 -0400
Subject: [Rd] transpose of complex matrices in R
In-Reply-To: <4C529CE0.2070408@cam.ac.uk>
References: <4C529CE0.2070408@cam.ac.uk>
Message-ID: <4C52A5C6.7080209@gmail.com>

Robin Hankin wrote:
> Hello everybody
>
> When one is working with complex matrices, "transpose"  very nearly 
> always means
> *Hermitian* transpose, that is, A[i,j] <- Conj(A[j,i]).
> One often writes A^* for the Hermitian transpose.
>
> I have only once seen a  "real-life" case
> where transposition does not occur simultaneously with complex conjugation.
> And I'm not 100% sure that that wasn't a mistake.
>
> Matlab and Octave sort of recognize this, as "A'" means the  Hermitian 
> transpose of "A".
>
> In R, this issue makes t(), crossprod(), and tcrossprod() pretty much 
> useless to me.
>
> OK, so what to do?  I have several options:
>
> 1.  define functions myt(), and mycrossprod() to get round the problem:
> myt <- function(x){t(Conj(x))}
>
> 2.  Try to redefine t.default():
>
>   t.default <- function(x){if(is.complex(x)){return(base::t(Conj(x)))} 
> else {return(base::t(x))}}
> (This fails because of infinite recursion, but I don't quite understand 
> why).
>   

You should call base::t.default, not base::t.  Then this will work.  The 
same solution fixes the one below, though you won't even need the base:: 
prefix on t.default.

Duncan Murdoch

> 3.  Try to define a t.complex() function:
> t.complex <- function(x){t(Conj(x))}
> (also fails because of recursion)
>
> 4. Try a kludgy workaround:
>    t.complex <- function(x){t(Re(x)) - 1i*t(Im(x))}
>
>
> Solution 1 is not good because it's easy to forget to use myt() rather 
> than t()
> and it does not seem to be  good OO practice.
>
> As Martin Maechler points out, solution 2 (even if it worked as desired)
> would break the code of everyone who writes a myt() function.
>
> Solution 3 fails and solution 4 is kludgy and inefficient.
>
> Does anyone have any better ideas?
>
>
>
>
>



[Rd] transpose of complex matrices in R
Duncan Murdoch