Re: [eigen] Matrix - Scalar CwiseUnaryOps |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Matrix - Scalar CwiseUnaryOps*From*: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>*Date*: Wed, 4 May 2011 08:55:03 -0400*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=XlJqEKm7Pb72cZ+6K5se0UZ9A2slSdIzhItPTlaeHn0=; b=WWYKO0U2TTeFrv3amkwgUNSxTPmLrnSGiBQ6vLzcLZavHU9GLJ+P/nqr+eLBERJ5up 4L1yPCDnupdVEfXg6uB2TA1jnSP9dLhwWDATE8CpAnTVN9+oI3PBdddogvtmjKliJlqP 5JEB0XOkHT6MVT7KWPZ0XpGLR632YvMfZPugo=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=nCHUGvTqwPYva+EEABvbSiwcjTUGy6Q+Z8RF8UjcHv7Y+oooY3A6xJ3yCRcOusnbBi CPhEL0q3gvuMpQ23cvjDj8+EMITJLIpEYPhG6TFt0FnvzDtNo0ffE0sh4Jh77Xac9nh1 x7Cb8WqxjMmfR3CE4Dxmqiw36lCKwPIJX7BCU=

Yes, the ambiguity is between interpreting a+M as 1) aE+M where E is the matrix all of whose coefficients are 1; this is what we do for arrays; or 2) aI + M where I is the identity matrix; this is definitely what mathematicians mean by a+M whenever they use that notation. This is required if you want basic matrix arithmetic rules to be self consistent, e.g. distributivity: (a+M)*N = aN + M*N This ambiguity is the primary reason why we leave this undefined in Eigen. Benoit 2011/5/4 Thomas Capricelli <orzel@xxxxxxxxxxxxxxx>: > > Hi, > > From a mathematical point of view a.M is defined but a+M is not... > (a=scalar, M=Matrix). > > my 2 cents.. > > Thomas > > -- > > Thomas Capricelli <orzel@xxxxxxxxxxxxxxx> > > http://www.freehackers.org/thomas > > On Wednesday 04 May 2011 11:39:13 Hauke Heibel wrote: > >> Hi, > >> > >> I know that we have the array functionality for those operations but I > >> wonder whether we should enable +/- operations between matrices and > >> scalars. > >> > >> We already have * and / and thus I think it might make sense. It's > >> just for convenience and I have met quite a few occasions where this > >> feature would lead to shorter code. What do you think? > >> > >> - Hauke > >> > >> > >> >

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**Re: [eigen] Matrix - Scalar CwiseUnaryOps***From:*Thomas Capricelli

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