Re: When is a List not a List?

*To*: mathgroup at smc.vnet.net*Subject*: [mg90959] Re: When is a List not a List?*From*: "news.individual.net" <noemail at noemail.com>*Date*: Fri, 1 Aug 2008 02:57:54 -0400 (EDT)*References*: <g6rntk$7kj$1@smc.vnet.net>

"AES" <siegman at stanford.edu> wrote in message news:g6rntk$7kj$1 at smc.vnet.net... > g[x_, n_] := x^n > FullForm[Table[g[x, n], {n, 1, 2}]] > FullForm[{g[x, 1], g[x, 2]}] > Plot[{g[x, 1], g[x, 2]}, {x, 0, 1}, PlotStyle -> {Red, Blue}] > Plot[Table[g[x, n], {n, 1, 2}], {x, 0, 1}, PlotStyle -> {Red, Blue}] > > The FullForm[]s are identical. One Plot[] has red and blue curves; the > other has two blue curves. > > Quirky! > Dear Pr. Siegman, This is indeed strange. It is related to the HoldAll attribute of Plot since by forcing the evaluation with Plot[Table[g[x, n], {n, 1, 2}] // Evaluate, {x, 0, 1}, PlotStyle -> {Red, Blue}] one gets two colors. By looking at the FullForm of the resulting graphics, with g1=Plot[{g[x, 1], g[x, 2]}, {x, 0, 1}, PlotStyle -> {Red, Blue}] we have for g1[[1]] a structure like {{{}, {}, {Hue[0.67, 0.6, 0.6], RGBColor[1, 0, 0], Line[{(*data points*)}]}, {Hue[0.906068, 0.6, 0.6], RGBColor[0, 0, 1], Line[{(* data points *)}]} }} which gives the two lines with different colors. For g2=Plot[Table[g[x, n], {n, 1, 2}], {x, 0, 1}, PlotStyle -> {Red, Blue}] we have for g2[[1]] {{{}, {}, {Hue[0.67, 0.6, 0.6], RGBColor[1, 0, 0], RGBColor[0, 0, 1], Line[{(* data points *)}], Line[{(* data points *)}]} }} where the two color directives are present, but the first line data is provided after the second color directive and is thus drawn with the same color as the second one... This is indeed quite strange. Guy Lamouche