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From: Dr Nathan Hurst <njh@nj...>  20100630 23:32:19

On Wed, Jun 30, 2010 at 04:01:06PM +0100, Maximilian Albert wrote: > 2010/6/30 <J.B.C.Engelen@...>: > > > I know what it does :), it meant to ask what it 'means', i.e. what is > > normalized? Perhaps normalize is a more general mathematical term than > > I thought. In any case, the question leads to whether the name of the > > function makes sense about what it does. To me, it did not, but perhaps > > that's just me. > > What does someone think when he reads that an SBasis object is > > 'normalized'? > > To be honest, I didn't have a clue when I read about normalizing an > SBasis object in your email (I didn't actually look at the code, > though). To me (coming from an algebraic background) normalizing a > polynomial means dividing by the coefficient of the highest > nonvanishing term (in Nathan's example this would result in x1/3). > But I have never heard about it in relation to 'throwing away terms > with coefficient zero'. So perhaps it's not just you. :) If people > don't have strong opinions on this I would suggest finding a more > descriptive name because the term 'normalize' is very overloaded in > mathematics. I don't have any good suggestions offhand, though. :/ Normalisation in general means removing all superfluous degrees of freedom to ensure that comparisons are simple, that the representation is compact, that false zeros do not confuse things. dividing out the leading coefficient is valid if you are root finding, as all polynomials that are scalar multiples of each other have the same root. So the first term is superfluous. However, for all other polynomial operations this is not true. But leading 0s in the representation are always superfluous. I'm not sure why we're having this discussion, normalise is not normally called by the user, it is used internally where cancelation might occur to prevent a blow out of leading zeros, or where a leading zero can break the algorithm. njh 
From: Maximilian Albert <maximilian.albert@go...>  20100630 15:01:16

2010/6/30 <J.B.C.Engelen@...>: > I know what it does :), it meant to ask what it 'means', i.e. what is > normalized? Perhaps normalize is a more general mathematical term than > I thought. In any case, the question leads to whether the name of the > function makes sense about what it does. To me, it did not, but perhaps > that's just me. > What does someone think when he reads that an SBasis object is > 'normalized'? To be honest, I didn't have a clue when I read about normalizing an SBasis object in your email (I didn't actually look at the code, though). To me (coming from an algebraic background) normalizing a polynomial means dividing by the coefficient of the highest nonvanishing term (in Nathan's example this would result in x1/3). But I have never heard about it in relation to 'throwing away terms with coefficient zero'. So perhaps it's not just you. :) If people don't have strong opinions on this I would suggest finding a more descriptive name because the term 'normalize' is very overloaded in mathematics. I don't have any good suggestions offhand, though. :/ Max 
From: <J.B.C.E<ngelen@ew...>  20100630 11:52:02

> Original Message > From: Dr Nathan Hurst [mailto:njh@...] > Sent: Wednesday, June 30, 2010 10:44 > To: Engelen, J.B.C. (Johan) > Cc: lib2geomdevel@...; zhenfeng.zhao.8@... > Subject: Re: [Lib2geomdevel] Normalizing a Pw<D2<SB>> > > On Wed, Jun 30, 2010 at 10:36:25AM +0200, > J.B.C.Engelen@... wrote: > > > (Inkscape uses its own copy of lib2geom. This means that Inkscape's > > lib2geom is not always uptodate. At the moment, since we > are close > > to release, Inkscape's lib2geom version is a little > outdated; notably > > Geom::Matrix has been renamed to Geom::Affine.) > > Actually, I have a merged version of all their changes, but > tweenk's Angle class is buggy (or at least it has different > assumptions to the svg elliptical arc code) and I haven't had > the fortitude to work out what the exact problem is. > > > > > When I look at SBasis::normalize() it does something quite > > > > different too. But that is because it is a 1D object, so > > > > normalizing the way I mean it does not make sense, right? > > > > > > It refers to removing unnecessary terms in the representation > > > (degree reduction). > > > > Yeah, I saw that. What does 'normalize' mean in this context? > > Consider 0x^3 + 0x^2 + 3x  1. The first two terms are > there, but they do not change the function at all. Normalise > would return 3x  1. I know what it does :), it meant to ask what it 'means', i.e. what is normalized? Perhaps normalize is a more general mathematical term than I thought. In any case, the question leads to whether the name of the function makes sense about what it does. To me, it did not, but perhaps that's just me. What does someone think when he reads that an SBasis object is 'normalized'? (after some googling, I read that indeed normalizing a polynomial means what the method says it means :) So forget about my comment :P Ciao, Johan 
From: Dr Nathan Hurst <njh@nj...>  20100630 08:44:16

On Wed, Jun 30, 2010 at 10:36:25AM +0200, J.B.C.Engelen@... wrote: > (Inkscape uses its own copy of lib2geom. This means that Inkscape's > lib2geom is not always uptodate. At the moment, since we are close to > release, Inkscape's lib2geom version is a little outdated; notably > Geom::Matrix has been renamed to Geom::Affine.) Actually, I have a merged version of all their changes, but tweenk's Angle class is buggy (or at least it has different assumptions to the svg elliptical arc code) and I haven't had the fortitude to work out what the exact problem is. > > > When I look at SBasis::normalize() it does something quite > > > different > > > too. But that is because it is a 1D object, so normalizing > > > the way I > > > mean it does not make sense, right? > > > > It refers to removing unnecessary terms in the representation > > (degree reduction). > > Yeah, I saw that. What does 'normalize' mean in this context? Consider 0x^3 + 0x^2 + 3x  1. The first two terms are there, but they do not change the function at all. Normalise would return 3x  1. njh 
From: <J.B.C.E<ngelen@ew...>  20100630 08:43:23

Hi all, I think we all lack time to invest in lib2geom, but I'd still like to propose a documentation sprint 'event'. Documentation sprint: pick a day on which we all work together to improve lib2geom's documentation (or perhaps code some extra functions that appear to be lacking). I think it will be a lot of fun seeing the work of others appear while you are working on the documentation yourself. By adding documentation, I mean adding doxygen stuff to the code. In the end we run doxygen and put it on lib2geom's website for reference. Krzysztof already added a lot of documentation, so there is plenty example of how to write doxygenstyle documentation. Because of time zones, a weekend day seems best, such that we can easily find a couple of hours where we are all available (and not working or sleeping). Let me know what you think, Johan 
From: <J.B.C.E<ngelen@ew...>  20100630 08:36:39

> Original Message > From: Dr Nathan Hurst [mailto:njh@...] > Sent: Wednesday, June 30, 2010 01:26 > To: Engelen, J.B.C. (Johan) > Cc: lib2geomdevel@...; zhenfeng.zhao.8@... > Subject: Re: [Lib2geomdevel] Normalizing a Pw<D2<SB>> > > On Wed, Jun 30, 2010 at 12:57:18AM +0200, > J.B.C.Engelen@... wrote: > > Hi all, > > > > ( Pw<D2<Sb>> means Piecewise<D2<SBasis> > ) > > > > Zhenfeng needs to get a path that contains the > normals/perpendicular > > to an input path: > > > > perpendicular = rot90(derivative(input_path)); > > > > However, the size of each (x,y) point of perpendicular path > should be > > unity, so the path has to be normalized. I think this is not yet > > possible in 2geom. > > perpendicular = unit_vector(rot90(derivative(input_path))) > > You might look at the offsettoy which does exactly this. Thanks for your rapid response Nathan! Zhenfeng: the "toys" Nathan is refering to are part of lib2geom's source code. You can find lib2geom at launchpad: https://launchpad.net/lib2geom And build instructions: http://tinkerhouse.net/log/lib2geomissweetstuff/ or http://wiki.inkscape.org/wiki/index.php/Lib2geom_FAQ >From reading the code, I see that 2geom's offsettoy does exactly what we want to achieve as a first step :) (Inkscape uses its own copy of lib2geom. This means that Inkscape's lib2geom is not always uptodate. At the moment, since we are close to release, Inkscape's lib2geom version is a little outdated; notably Geom::Matrix has been renamed to Geom::Affine.) > > When I look at SBasis::normalize() it does something quite > > different > > too. But that is because it is a 1D object, so normalizing > > the way I > > mean it does not make sense, right? > > It refers to removing unnecessary terms in the representation > (degree reduction). Yeah, I saw that. What does 'normalize' mean in this context? Ciao, Johan 
From: Dr Nathan Hurst <njh@nj...>  20100629 23:44:16

On Wed, Jun 30, 2010 at 12:57:18AM +0200, J.B.C.Engelen@... wrote: > Hi all, > > ( Pw<D2<Sb>> means Piecewise<D2<SBasis> > ) > > Zhenfeng needs to get a path that contains the normals/perpendicular to > an input path: > > perpendicular = rot90(derivative(input_path)); > > However, the size of each (x,y) point of perpendicular path should be > unity, so the path has to be normalized. I think this is not yet > possible in 2geom. perpendicular = unit_vector(rot90(derivative(input_path))) You might look at the offsettoy which does exactly this. > When I look at SBasis::normalize() it does something quite different > too. But that is because it is a 1D object, so normalizing the way I > mean it does not make sense, right? It refers to removing unnecessary terms in the representation (degree reduction). njh 
From: <J.B.C.E<ngelen@ew...>  20100629 22:57:56

Hi all, ( Pw<D2<Sb>> means Piecewise<D2<SBasis> > ) Zhenfeng needs to get a path that contains the normals/perpendicular to an input path: perpendicular = rot90(derivative(input_path)); However, the size of each (x,y) point of perpendicular path should be unity, so the path has to be normalized. I think this is not yet possible in 2geom. When I look at SBasis::normalize() it does something quite different too. But that is because it is a 1D object, so normalizing the way I mean it does not make sense, right? Would someone be willing to help me implement a normalize method for paths? Thanks a bunch! Johan 
From: <J.B.C.E<ngelen@ew...>  20100602 22:30:32

Hi all, This summer, Zhenfeng will work on a new "variable stroke width" LivePathEffect, called "Power Stroke". Now that Zhenfeng has started his GSoC, I'd like all who are interested to join the discussion on this page: http://wiki.inkscape.org/wiki/index.php/PowerStroke#Discussion_at_LGM_20 . Already I got some great input at the Libre Graphics Meeting in Brussels last week. More input is always welcome. Thanks a lot! Johan 