Re: Re: What's going on here (Table-generated lists)?

*To*: mathgroup at smc.vnet.net*Subject*: [mg98152] Re: [mg98104] Re: What's going on here (Table-generated lists)?*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Tue, 31 Mar 2009 04:20:53 -0500 (EST)*References*: <gqn8ua$p$1@smc.vnet.net> <200903300943.EAA08071@smc.vnet.net>*Reply-to*: drmajorbob at bigfoot.com

It's not entirely unavoidable, but there are cases where it's almost so. For instance, Plot[x /. Solve[x^3 - x^2 + b x + 1 == 0, x], {b, -5, 5}] For different b values there are 1, 2, or 3 solutions. Colors COULD be assigned after the points are calculated, but what colors should be used, and where? Or look at the colors in the evaluated version: Plot[x /. Solve[x^3 - x^2 + b x + 1 == 0, x]//Evaluate, {b, -5, 5}] Bobby On Mon, 30 Mar 2009 04:43:52 -0500, AES <siegman at stanford.edu> wrote: > In article <gqn8ua$p$1 at smc.vnet.net>, > Bill Rowe <readnews at sbcglobal.net> wrote: > >> >I still don't see why it doesn't make sense >> >for Plot to recognize a list as an actual list and plot each with a >> >different color. >> >> Plot does this when the argument provided is a list, That is >> >> Plot[{x,x^2},{x,0,1}] >> >> will plot two curves in two different colors. > > But > > Plot[0.5{x,x^2}, {x,0,1}] > > will not plot two curves in two different colors -- right? -- > despite the fact that evaluating 0.5{x,x^2} by itself > displays as {0.5 x, 0.5 x^2} ); and > > Plot[{0.5x, 0.5x^2}, {x, 0, 1}] > > does plot two curves in two different colors > >> What answer are you looking for here? > > In my case (I'm not the OP), not an explanation of why this happens > (I've come to sort of understand this); but as purely curiosity > questions (since this behavior of Plot comes up time after time): > > 1) Is having this weird and confusing behavior in the Plot[] command > somehow necessary, unavoidable, for reasons deep in the fundamental > structure of Mathematica? -- or is this merely a bad design choice made > long ago, that one would wish could now be extirpated (but probably > can't be)? > > 2) Does Wolfram have any understanding of how much the string of > endless "gotchas" like this damage the usability of Mathematica for > ordinary users (as contrasted to full time professional programmers)? > > 3) Should maybe evaluating 0.5{x,x^2} by itself display as > > { {0.5 x, 0.5 x^2} } > > since that's what it really is? (Or should Plot[] maybe strip off the > outer { }'s if given this as the function to be plotted?) > -- DrMajorBob at bigfoot.com

**References**:**Re: What's going on here (Table-generated lists)?***From:*AES <siegman@stanford.edu>