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I have a compiled function which I can plot without issue using Plot. However, when I use LogLinearPlot I get the message:

Argument x at position 1 should be a machine-size real number.

The following MWE gets the same message:

compFn = Compile[{{x, _Real}}, x^2 + 2]
LogLinearPlot[compFn[x], {x, 1, 100}]

Ultimately my goal is to plot the function with a logarithmic scale for the $ x $-axis.

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  • $\begingroup$ does this work as a work-around: Plot[cf[x], {x, 0, 100}, ScalingFunctions -> {{Log, Exp}, None}]? $\endgroup$
    – kglr
    May 27, 2018 at 11:44
  • $\begingroup$ .. or this: Plot[cf[Exp@x], {x, Log@1, Log@100}, Ticks -> {Charting`ScaledTicks[{Log, Exp}], Automatic}]? $\endgroup$
    – kglr
    May 27, 2018 at 11:48
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    $\begingroup$ What version and OS are you using? Your code works as expected with v11.3 on a Mac. $\endgroup$
    – Bob Hanlon
    May 27, 2018 at 12:44
  • $\begingroup$ A wild guess, maybe you need to Clear[x]. BTW, your code runs no warning and no error on my side. $\endgroup$
    – Αλέξανδρος Ζεγγ
    May 27, 2018 at 12:48
  • $\begingroup$ @BobHanlon Windows 10 and Mathematica 10.2. I have v11 on another computer so may try to transfer it over and run it there. $\endgroup$
    – atom44
    May 28, 2018 at 10:09

2 Answers 2

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In 11.3, your code works without issue. I guess in an earlier version, Mathematica might try to evaluate your compiled function with a symbolic x which leads to the error. Try the following, which wraps your compiled code in a function that does only allow numerical values

With[{compFn = Compile[{{x, _Real}}, x^2 + 2]},
  f[x_?NumericQ] := compFn[x]
  ];
LogLinearPlot[f[x], {x, 1, 100}]

Mathematica graphics

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  • $\begingroup$ This worked for me. Thanks! $\endgroup$
    – atom44
    May 28, 2018 at 10:10
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In MMA 11 code is working.

compFn = Compile[{{x, _Real}}, x^2 + 2]
LogLinearPlot[compFn[x], {x, 1, 100}, Frame -> True, PlotStyle -> Blue,
     FrameStyle -> Directive[Black, Thick], PlotRange -> All]

plot

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