Re: [eigen] Sign function |

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*To*: eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: Re: [eigen] Sign function*From*: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>*Date*: Sat, 8 Dec 2012 17:12:26 +0100*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; bh=moMx1n14+79kIcij4gXorET+IxoW93gbSEQc2RLxS+s=; b=fBYL/69HSYRr7mHseFZ9CueiZjGEcg3gTHgzWbfMWFmrP5Z5zHKzSJmH3aTGcR52dM Ddi9BldxjqSFdPDX2AaX8YPP35aZL5cpRKKdQBajDwb4l4Bt5+PyhxN//Je4gnehnk0V aWZhU72VRukq14VosSdI0w9KXyY9yfecKAuyEm54rZR+nK4VVFyicYnLDhWE8/pQq2vp wAMYTEVXa/tVMXW6tWr/k+C/of3Zu8x3I2Q/sLox2NmVriaBqTgUgwNim5eT5Y8LRGXs HK4JbQ4YCyYWrdWe01E9XL6aJ8rFKzBYBke67ED1bEc1l8h1lcUsIBCGDYtfvbLZLyCD IeSw==

Actually it is rather MatType::Constant(rows,cols,k), and this is an _expression_, so no allocation at all.

On Sat, Dec 8, 2012 at 3:13 PM, Carlos Becker <carlosbecker@xxxxxxxxx> wrote:

Hi Gael,thanks!If MatType is something 'huge' in the example you gave, would it get instantiated in memory? because then I should probably use another way of doing it.For example, I would replace MatType::Constant(k) with VectorXd::Constant( N, k ), where N could be pretty large.thanks again.

------------------------------------------Carlos

On Sat, Dec 8, 2012 at 2:08 PM, Gael Guennebaud <gael.guennebaud@xxxxxxxxx> wrote:You can do something like:A += (B.array()>0)..select(MatType::Constant(k),-k);Unfortunately the following cannot work because we have to know the matrix type returned by select from at least one of its arguments:A += (B.array()>0).select(k,-k);You can also use B.unaryExpr(std::ptr_fun(sign)) to reproduce "sign(B)".gaelOn Sat, Dec 8, 2012 at 12:26 PM, Carlos Becker <carlosbecker@xxxxxxxxx> wrote:Hello everyone,I am wondering which would be the fast way to compute the sign of every element in a vector or matrix, since I have to do the following element-wise:A = A + k * sign(B)where A and B are double matrices and k is a scalar.I was trying to find some information in the docs but so far I didn't succeed.I know I can do a boolean operation and then cast to double, multiply by 2 and subtract 1, but that doesn't seem very efficient.Maybe some kind of custom element-wise processing, since it would be enough to compute the sign and then add k or -k to each element of A ?Thanks!

**Follow-Ups**:**Re: [eigen] Sign function***From:*Carlos Becker

**References**:**[eigen] Sign function***From:*Carlos Becker

**Re: [eigen] Sign function***From:*Gael Guennebaud

**Re: [eigen] Sign function***From:*Carlos Becker

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