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I have the following function

f[z_] := Piecewise[{{Cos[z] - 17 Sin[z]/z, z > 0}, {Cosh[z] - 17 Sinh[z]/z, z <= 0}}]

I am interested in the regions where $\vert f(z)\vert \leq 1$, I tried to shade that region using Filling, but my results were not the expected, how should I write the code? Here is my attempt: 

Plot[{f[z], -1, 1}, {z, -5, 20}, PlotStyle -> {Automatic, Dashed, Dashed}, Filling -> {1 -> {3}}]

enter image description here

To be more precise: I want to shade the region $D=\{(x,y):\vert f(x) \vert<1\text{ and } \vert y \vert <1 \}$

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  • $\begingroup$ Is this not what you want: Filling -> {2 -> {3}} ? $\endgroup$ – Arnoud Buzing Apr 17 '20 at 20:58
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    $\begingroup$ does Plot[{f[z], ConditionalExpression[f[z], -1 < f[z] < 1], -1, 1}, {z, -25, 20}, PlotStyle -> {Automatic, None, Dashed, Dashed}, Filling -> {2 -> {{3}, Cyan}, 2 -> {{4}, Cyan}}, PlotPoints -> 100] give what you need? $\endgroup$ – kglr Apr 17 '20 at 22:20
  • $\begingroup$ .. or Plot[{f[z], ConditionalExpression[f[z], -1 < f[z] < 1], -1, 1}, {z, -25, 20}, PlotStyle -> {Automatic, None, Dashed, Dashed}, Filling -> {2 -> {Axis, Cyan}}, PlotPoints -> 100]? $\endgroup$ – kglr Apr 17 '20 at 22:21
  • $\begingroup$ @kglr Yes! That is what I wanted, Thanks! $\endgroup$ – Victor Gustavo May Apr 17 '20 at 22:22
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Plot[{f[z], ConditionalExpression[f[z], -1 < f[z] < 1], -1, 1}, {z, -25, 20}, 
 PlotStyle -> {Automatic, None, Dashed, Dashed}, 
 Filling -> {2 -> {{3}, Cyan}, 2 -> {{4}, Cyan}}, PlotPoints -> 100]

enter image description here

Also

Plot[{f[z], Clip[f[z], {-1, 1}, {Null, Null}], -1, 1}, {z, -25, 20}, 
 PlotStyle -> {Automatic, None, Dashed, Dashed}, 
 Filling -> {2 -> {{3}, Cyan}, 2 -> {{4}, Cyan}}, PlotPoints -> 100]

same picture

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If the answer to my question in the comments is 'no', then perhaps this:

Plot[{f[z], Clip[f[z]], -1, 1}, {z, -25, 20}, 
 PlotStyle -> {Automatic, None, Dashed, Dashed}, 
 Filling -> {2 -> Axis}]

enter image description here

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  • $\begingroup$ This is not quite what I am looking for, I edited my question to be more precise regarding the region I wish to shade $\endgroup$ – Victor Gustavo May Apr 17 '20 at 21:47

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