RE: Problems using Legend whith LogPlot and LogPlotPlot

*To*: mathgroup at smc.vnet.net*Subject*: [mg36844] RE: [mg36827] Problems using Legend whith LogPlot and LogPlotPlot*From*: "David Park" <djmp at earthlink.net>*Date*: Sun, 29 Sep 2002 02:55:02 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Awk! Legends! Basically, the answer to your question is that the PlotLegend option works ONLY for the Plot command and does not work for other types of plots. For other types of plots you have to use ShowLegend. And ShowLegend is not all that easy to use, especially since WRI does not give an example for multiple curves in the Help. Needs["Graphics`Graphics`"] Needs["Graphics`Legend`"] {q1[t_], q2[t_], q3[t_]} = {0.1 Exp[-0.02 t], 0.2 Exp[-0.025 t], 0.4 Exp[-0.028 t]}; Let's look at your first plot. Plot[{q1[t], q2[t], q3[t]}, {t, 0, 100}, PlotStyle -> {{AbsoluteThickness[0.5], AbsoluteDashing[{4, 4}]}, AbsoluteThickness[1.5], {AbsoluteThickness[2], AbsoluteDashing[{1, 8}]}}, AxesLabel -> {"Y", "X"}, PlotLabel -> "Title", PlotLegend -> {"1", "3", "5"}, LegendPosition -> {0.5, 0}, ImageSize -> 500]; The legend is almost as big as the plot. It distracts from the real information you are trying to convey. Furthermore, the order of the curves in the legend is the reverse of their order in the plot. The following shows how to put the legend in a LogLogPlot, or other types of plots. I defined the plot styles independently because they are used in several places. I made the legend much smaller and put it in an empty area of the plot. I also reversed the order of the keys so they would match the order of the curves in the plot. styles={{AbsoluteThickness[0.5], AbsoluteDashing[{4,4}]},{AbsoluteThickness[1.5]},{AbsoluteThickness[ 2],AbsoluteDashing[{1,8}]}}; ShowLegend[ LogLogPlot[{q1[t], q2[t], q3[t]}, {t, 0, 100}, PlotStyle -> styles, AxesLabel -> {"Y", "X"}, PlotLabel -> "Title", ImageSize -> 500, DisplayFunction -> Identity], {MapThread[{Graphics[{Sequence @@ #1, Line[{{0, 0}, {1, 0}}]}], #2} &, {styles, {1, 3, 5}}] // Reverse, LegendPosition -> {-0.7, -0.4}, LegendSize -> {0.2, 0.3}, LegendShadow -> {0.02, -0.02}, LegendSpacing -> 0.5} ]; But why use a legend at all? After all, a legend is nothing but another plot in which you have put labels on the curves. Why not put the labels directly on the curves in the real plot in the first place? LogLogPlot[{q1[t], q2[t], q3[t]}, {t, 0, 100}, PlotStyle -> styles, AxesLabel -> {"Y", "X"}, PlotLabel -> "Title", ImageSize -> 500, Epilog -> MapThread[ Text[SequenceForm["Case ", #1], {Log[10, 0.01], Log[10, #2[0.01]]}, {0, -1}] &, {{1, 2, 3}, {q1, q2, q3}}]]; In the legend you have keyed the curves to numbers 1, 3 and 5. (Perhaps you just used these as examples and meant to use something different in the real plots?) But these don't seem to have any obvious relation to your functions. I suppose the reader will have to look at another table or look into the text of your paper or notebook to find out what 1, 3 and 5 mean. So the reader has to go from the graph to the legend then to the text and then mentally transfer the meaning of the curve back to the main plot. It is so much nicer to put the meaning right on the curve if you can. For the most part, legends are just "computer junk" and not even easy to nicely construct. When the legend urge comes over you - try to resist. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: guillerm at usal.es [mailto:guillerm at usal.es] To: mathgroup at smc.vnet.net Dear friends I have the following problem with Legend and LogPlot and LogPlotPlot: Needs["Graphics`Graphics`"] Needs["Graphics`Legend`"] {q1[t_],q2[t_],q3[t_]}={0.1 Exp[-0.02 t], 0.2 Exp[-0.025 t], 0.4 Exp[-0.028 t]}; (*With Plot legend works fine*) Plot[{q1[t],q2[t],q3[t]}, {t, 0, 100},PlotStyle\[Rule]{ {AbsoluteThickness[0.5], AbsoluteDashing[{4,4}]}, AbsoluteThickness[1.5], {AbsoluteThickness[2], AbsoluteDashing[{1,8}]}}, AxesLabel\[Rule]{"Y", "X"}, PlotLabel\[Rule]"Title", PlotLegend\[Rule]{"1","3","5"}, LegendPosition\[Rule] {0.5,0}] (*However with LogPlot or LogLogPlot the legend desappear*) LogLogPlot[{q1[t],q2[t],q3[t]}, {t, 0, 100},PlotStyle\[Rule]{ {AbsoluteThickness[0.5], AbsoluteDashing[{4,4}]}, AbsoluteThickness[1.5], {AbsoluteThickness[2], AbsoluteDashing[{1,8}]}}, AxesLabel\[Rule]{"Y", "X"}, PlotLabel\[Rule]"Title", PlotLegend\[Rule]{"1","3","5"}, LegendPosition\[Rule] {0.5,0}] I have shown a particular case, but I has this problem always with Legend and LogPlot and LogPlotPlot. I will appreciate any help. Thanks Guillermo Sanchez --------------------------------------------- This message was sent using Endymion MailMan. http://www.endymion.com/products/mailman/