Re: [eigen] Treat single-element Array as scalar for arithmetc operations |

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*To*: eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: Re: [eigen] Treat single-element Array as scalar for arithmetc operations*From*: Rasmus Munk Larsen <rmlarsen@xxxxxxxxxx>*Date*: Tue, 28 Jul 2020 18:56:40 -0700*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=cboHO+OyZecKkhtZ+mEXMCpZ+Jyf+vR7r70S9PwGSNk=; b=PoXL/2FFxY+Hg4bwe3PmHivFChYCarQKfLSJ6tNNduzkQvni68qeDO6gnbH9ejOmee o2jYXIosOPijKJ6/6yBzAkkaoUfPg3fLy0zHsZXrBIqkYI6hbN2UL6tlbUy8Np+4NARx C9l/4qPPxQ58QvPrgWaRCwz07KnRAgl09m6WV2bpoN5Yq6Z5imBkevyqMx+Pj4JvAifl GINEOX+GCVsdarwMFXY9U3SCmxG1Ei2XcPwCiJ6KnWp80Ungltj8Hzuaoequ9OhAo77p 4EM1xKPxroqubdZjCd5dSVLiMU/MAAFj6exxh9pia+BG12BvkKg9qsu5ItJmTbMYFCSp TdXA==

Generally speaking, silently treating vectors as scalars and vice versa with implied broadcasting is a common source of subtle bugs, so this behavior is unlikely to change. Eigen does support scalar*vector, if you extract the single element as such.

On Tue, Jul 28, 2020 at 6:06 AM Mario Azcueta <mazcueta@xxxxxxxxx> wrote:

Is there a way of adding/subtracting/multiplying two Eigen::ArrayXd arrays both when (a) they have dimension N, and (b) when one of them has dimension N and the other dimension 1?I'd ideally like that the array with size=1 is treated like a scalar for these operations. I'm somewhat trying to replicate the way Matlab behaves.As an example, I'd the code below to work both when a1 and a2 have the same size, as well as when one of them has size=1 and the other size=N:

ArrayXd add_arrays(const ArrayXd& a1, const ArrayXd& a2)

{

return a1 + a2;

}

Of course, this could be solved with an if statement, but I want to avoid that since my actual code would require to write a long function verifying all combinations of sizes (they're many args). Also, writing a template function gets me problems when trying to use some ArrayXd methods and I pass a double.I've looked into the EIGEN_ARRAYBASE_PLUGIN preprocessor which may seem like the way to extend this behavior, but I'm not sure this is the right way.. any advice will be welcome.Note: I've also post this question herehttps://stackoverflow.com/questions/63074198/c-eigen-treat-single-element-array-as-scalar-for-arithmetc-operations

**Follow-Ups**:**Re: [eigen] Treat single-element Array as scalar for arithmetc operations***From:*Joseph Mirabel

**References**:**[eigen] Treat single-element Array as scalar for arithmetc operations***From:*Mario Azcueta

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