Mark McClure
Reputation
25,044
200/100 score
 Sep 23 comment getting vertices in order from spanning tree I get a sequence of errors of the form: Function::flpar: Parameter specification Append[vlist,#1] in Function[Append[vlist,#1],1] should be a symbol or a list of symbols. >> I guess this can be fixed using SetDelayed rather than Set. Sep 23 comment Combining many plots with Show produces wrong x-axis position and wrong filling The problem is that the filling is generated to fit within each individual plot range. So just set the PlotRange in each of the plots individually, rather than just in the Show command. That way, the filling will fill the whole common plot range. Sep 19 comment Understanding differences between Maple and Mathematica in examples picked by Maplesoft @DanielLichtblau Oops - better? Sep 18 comment Short form of Graphics Sorry, I posted a comment since I looked at your post quite quickly. Does Plot[x, {x, 0, 1}] // Options help? Sep 18 comment Short form of Graphics How about Plot[x, {x, 0, 1}] // InputForm // Short? Or, if you need more control, Short[InputForm[Plot[x, {x, 0, 1}]], 10]. Sep 17 comment Kernel crashes when plotting $z=\sqrt{(x^2 + y^2)}^0$ @Mr.Wizard Yeah, I'm fine with that. Sep 17 comment Kernel crashes when plotting $z=\sqrt{(x^2 + y^2)}^0$ @Mr.Wizard I flagged it as such but did not downvote. Both "answers" seem to be simple comments to me but I can't say that I feel strongly enough to make a meta post. Sep 15 comment How to manipulate a circle in GeoGebra style? Personally, I preferred the original circle based version - which garnered my upvote. While it didn't replicate the GeoGebra behavior exactly, it certainly got the same idea across and with much simpler code. Furthermore, it's not clear from the question that an exact replication was necessary - at least not to me. Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions @belisarius Your question seems to be exactly opposite of the one here - namely, Plot[Derivative[f]...] uses a finite difference scheme on discrete functions, such as IntegerPart, Round and several others. Sep 12 comment Speed of ConvexHullMesh So, should the question be closed? Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions Incidentally, Derivative is not protected, so you can easily define your own DownValues: Thus, Abs'[x_] := Sign[x]; Abs'[0.5] produces 1. Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions Well, I guess it's not just D but the general fact that symbolic computation assumes symbols are complex. Many computations performed by Mathematica must be fully understood in this context - from Simplify[Abs[x^2]] to the apparent missing branch of the cube root in Plot[x^(1/3), {x,-1,1}]. There are exceptions, particularly the CubeRoot and Surd functions introduced in V9 but, generally, computations are done in the complex numbers and I assure you that this is the context in which you need to explore your question. Sep 12 comment Solve Laplace equation using NDSolve @SantiCarmesí The gradient field issue is discussed in great detail here. Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions A similar thing happens with Re and Im. While those functions are obviously meant to work in the complex realm, I think an understanding of what is going on there is relevant. This discussion might help in that regard. Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions It really doesn't matter if you agree or not - the basic fact is that D works in the complex domain and these functions are not differentiable in that context. That, quite simply, is the explanation of the behavior you see. Now, whether you would prefer different behavior and how you might implement it is a different question. Sep 12 comment Strange behaviour of MMA in derivatives of some standard functions The functions you explore are all non-analytic as complex functions, thus the derivative is undefined. You might explore the numerical derivative ND as defined the NumericalCalculus package. Sep 11 comment Homotopy Visualization I did something like here to illustrate graph isomorphism. That's much simpler, though, really. Shouldn't be to hard to grab a set of points describing the boundaries of the objects but it might be tricky to maintain the topological integrity throughout the animation. Sep 11 comment Homotopy Visualization I guess you mean a homotopy, actually. Sep 10 comment How do I plot the images of oriented curves under complex transformation? How about Show[r1, r1 /. Line[pts_] :> Arrow[pts, 2]]? Sep 9 comment Calculating a potential function using the finite element method @Hugh There certainly are other ways to make a mesh. In this answer I show how to interface with a free, third party program called triangle that might do what you want. However, I'd think that converting them to the ElementMesh format that you want would be rather involved. Also, V10.0.1 is due out any day and I'm quite certain that bugs in mesh generation have been addressed, though I'm not certain if this specific issue is improved or not. Will definitely be worth checking out, though.