# Combining Multiple Contour Plots with Different X, Y, and Z Ranges

I am trying to calculate the differences in natural frequencies between two different dynamic models, and I would like to plot these error contours in terms of ues (mass ratio) and nel (frequency ratio). err1 corresponds to the error when nel > 1 and err2 corresponds to the error when nel < 1.

Naturally these error contours should be plotted on a single graph, but I cannot find a way to combine these on a single graph, especially since nel needs to be plotted on a log X-axis. I have tried Show[], but I cannot get it to plot the graph with the following requirements:

1. Logarithmic X-axis (ues)
2. Filled in Contours
3. Contour Plot Range (error) shall be {0 , 0.5}
4. X-Axis (ues) Range shall be {0 , 1}
5. Y-Axis (nes) Range shall be {0 , 3.5}

Here are two separate graphs that accomplish the requirements above but are not combined:

ClearAll["Global*"]

err1 = -1 + Sqrt[2]/Sqrt[1 + ues + nel^2*(1 + ues) -
Sqrt[(1 + ues)*((-1 + nel^2)^2 + (1 + nel^2)^2*
ues)]]

err2 = 1 - Sqrt[2]/Sqrt[1 + ues + nel^2*(1 + ues) +
Sqrt[(1 + ues)*((-1 + nel^2)^2 + (1 + nel^2)^2*
ues)]]

(* Plot Error 1 Contour *)
Show[ContourPlot[
Tooltip[err1, Row[{"ues = ", ues}]], {ues, 0, 1}, {nel, 1, 3.5},
PlotRange -> {0, 0.501},
Contours -> Join[{0.01}, Range[0.05, 0.50, 0.05]],
AxesLabel -> Automatic, ScalingFunctions -> {"Log", None}],
AxesLabel -> {None, None},
FrameLabel -> {{HoldForm[nel], None}, {HoldForm[ues], None}},
PlotLabel -> None, LabelStyle -> {GrayLevel[0]}]

(* Plot Error 2 Contour *)
Show[ContourPlot[
Tooltip[err2, Row[{"ues = ", ues}]], {ues, 0, 1}, {nel, 0, 1},
PlotRange -> {0, 0.501},
Contours -> Join[{0.01}, Range[0.05, 0.50, 0.05]],
AxesLabel -> Automatic, ScalingFunctions -> {"Log", None}],
AxesLabel -> {None, None},
FrameLabel -> {{HoldForm[nel], None}, {HoldForm[ues], None}},
PlotLabel -> None, LabelStyle -> {GrayLevel[0]}]


Note I use ScalingFunctions from Mathematica 11.

 ContourPlot[Tooltip[If[nel <= 1, err2, err1], Row[{"ues = ", ues}]],

• Both If or Piecewise` work beautifully. Thanks for showing me a path foward. – felimz Oct 14 '18 at 23:00