>> I reiterate that in polar coordinates, a negative value of "r" does not make >> sense. It is confusing at best. > > This isn't really true. Many standard introductions to polar > coordinates consider negative r as valid. It's simply treated as a > radius in the opposite direction
In Euclidean space, can you have a negative distance? Would you ever describe a circle as having negative radius (in Euclidean space)? If you take "r" to be the radius, then I suggest you confuse a precise definition of radius with allowing a useful, non-unique interpretation of negative values of "r". > (i.e., the point is reflected about > the origin). A few examples found by googling: > http://tutorial.math.lamar.edu/Classes/CalcII/PolarCoordinates.aspx > and > http://sites.csn.edu/istewart/mathweb/math127/intro_polar/intro_polar.htm > and an MIT Opencourseware document at > http://ocw.mit.edu/resources/res-18-001-calculus-online-textbook-spring-2005/study-guide/MITRES_18_001_guide9.pdf. > The nice MIT notes you linked to state (sec. 9.2, (page 355) listed as 132 on the bottom of page) "The polar equation r = F(theta) is like y = f(x). For each angle theta the equation tells us the distance r (which is not allowed to be negative)." > Matplotlib shouldn't raise an error on negative r, it should just > interpret negative r values correctly. You assume all people have chosen the same definition of how to interpret negative values of "r". I grant you that it may be useful in some contexts to define what it means to have negative values of "r". But this definition is NOT UNIQUE. However, if you take "r" as a radius, and hence a positive definite quantity, as you would expect in Euclidean geometry for a distance, and you allow r: [0,inf] theta: [0,2pi) then there is a unique and unambiguous representation of the coordinates. I am not arguing that one can not take a definition of negative "r", only that different users will expect different things, and what matplotlib choses to do is not readily accessible in the documents as far as I can see. I also argue that many users, coming from the scientific background, will naturally interpret "r" as the radius (as I do) and hence expect "r" to be positive definite. And lastly, I argue, that since the definition is not unique, and people have different expectations, at the very least, matplotlib should warn you how it is interpreting negative "r". Regards, Andre ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
