Re: [eigen] Overflow in sum() |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Overflow in sum()*From*: Christian Mayer <mail@xxxxxxxxxxxxxxxxx>*Date*: Wed, 01 Apr 2009 21:29:40 +0200*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:sender:message-id:date:from :reply-to:user-agent:mime-version:to:subject:references:in-reply-to :x-enigmail-version:content-type:content-transfer-encoding; bh=DBjdMFJSRXsbiG/Ltf1a5FunE54ADxmq0XFpjpOxXhs=; b=GSG4aYUQluHInTFflytHtdFI63JaistCeJFyd0mfq2Fq4eJqSpo+GFOVXoJYyGxcgz Vi1Uc/bUb3iq/sjZiaPlNH49+Llv8yF8oGhsDJKwTPVW49GtIuZiv1aKHFrk7L5XbnNZ 7KKDKisDZvDue9yg1PWqL9CB5IKmFT3JWGu/E=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:message-id:date:from:reply-to:user-agent:mime-version:to :subject:references:in-reply-to:x-enigmail-version:content-type :content-transfer-encoding; b=m1JOxw8GmmPF5scydSOKbgdGgECWXCEF9ZQ4sSumwLN6z0JsiLz/bdDk3QhrDYtJed elkzDGt1QYO6R/y4mrH1/+Q/rXLH7dmSz0sf6DuadrQ7kCtjSUGvrzO5DwZMBvLLWtPz QzdM0T+Eq4n3SkAmivoinp5wXkVYu2Uue1aPk=

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Benoit Jacob schrieb: > ah that's yet another different problem... > > with sparse matrices, the overflow problem arises only with a few > operations like sum(). > > But with what you say, dense matrices of uint8, the overflow can > happen with a lot more operations: for example, any matrix product > will typically overflow! So I guess that a matrix product of unit8 > matrices should return a matrix with a bigger scalar type... I'm working in the area of embedded software development where huge amounts of numerical software has to be dealt with in real time. As some of that code is quite old it's mostly written in fixed point, i.e. it's using normal integer operations (the variables usually have to be multiplied by a factor and an offset has to be added to get the "real world meaning" of each variable). In this context lots of programmers are looking for data types and possible overflows just to handle that problem, as each multiplication and addition could cause a problem. And there are usually two solutions: saturate or clip (i.e. just use the modulo value). => that's too far for eigen to handle But it might be a nice solution to offer (as a template parameter) a different data type as an result, so that the eigen user can handle this requirement each time it could appear in the best way for his algorithm. (And if possible we could also offer an saturating and an clipping version of the algorithm) CU, Chris -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEAREIAAYFAknTwKMACgkQoWM1JLkHou3scwCfSlLGepOwfZHX7/2a+X7de/MC eZcAn2a0doVjFW4/M8witEbO0Op8HWPI =eZE/ -----END PGP SIGNATURE-----

**Follow-Ups**:**Re: [eigen] Overflow in sum()***From:*Benoit Jacob

**References**:**[eigen] Overflow in sum()***From:*Jens Mueller

**Re: [eigen] Overflow in sum()***From:*Benoit Jacob

**Re: [eigen] Overflow in sum()***From:*Patrick Mihelich

**Re: [eigen] Overflow in sum()***From:*Benoit Jacob

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