Re: LogLogPlot encounters Infinite expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg126163] Re: LogLogPlot encounters Infinite expression*From*: "djmpark" <djmpark at comcast.net>*Date*: Sun, 22 Apr 2012 06:06:00 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <581857.12253.1334983314299.JavaMail.root@m06>

This looks like a bug in the internal initial processing for LogLogPlot, possibly in trying to determine the y axis Range - although I don't know why it would do that first. If one does the following, the routine never samples outside of the specified domain. f[x_] := Piecewise[{{0.001, x < 10}}, Exp[x/20]] Reap[LogLogPlot[1/f[x], {x, 11, 20}, EvaluationMonitor :> Sow[x]]] If we change back to zero, it bombs before sowing any x values. The simplest solution is to modify the plot function for the purpose of this particular plot. LogLogPlot[1/Exp[x/20], {x, 11, 20}] With the Presentations Application you could specify the ticks and roll your own LogLog curve with some extra work but without having to modify the f function. << Presentations` xticks = CustomTicks[Log, {1, 2, {12, 14, 16, 18, 20}/10, {}}]; yticks = CustomTicks[Log, {-1, 0, Range[3.5, 6, 0.5], {}}]; Draw2D[ {Draw[Log[1/f[E^logx]], {logx, Log[11], Log[20]}]}, AspectRatio -> 0.6, Axes -> True, Ticks -> {xticks, yticks}] David Park djmpark at comcast.net http://home.comcast.net/~djmpark/index.html From: John_V [mailto:jvillar.john at gmail.com] If I try this: f[x_] = Piecewise[{{0, x < 10}}, Exp[x/20]] LogLogPlot[1/f[x], {x, 11, 20}] the result is an error message (Infinite expression 1/0 encountered) and a plot that has axes but no graph. Notice that although 1/f is indeed 1/0 for x<10, the requested plot range does not include x<10. The function is well-defined within the requested plot range. Does anyone know what's going on with this? John