# How to plot a single variable function with constraints

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Mihai Giurca on 20 Mar 2020
Edited: Matt J on 20 Mar 2020
Hello, I am trying to plot f(x) = 4 - x*sin(x) with constraints x>=6, x<=9 and log(x)>= -1. I tried using meshgrid but the graph came out wrong + it was in the 3rd dimension. Can anyone tell me how I should go about plotting a simple function with these constraints? Thank you!

Ameer Hamza on 20 Mar 2020
What does the constraint log(x)>= -1 mean? Does it mean x >= exp(-1)? How does this combine with x>=6, x<=9?
Mihai Giurca on 20 Mar 2020
I'm honestly not sure, my professor gave me these constraints and I'm not sure what the log is supposed to mean.

Ameer Hamza on 20 Mar 2020
f = @(x) 4 - x*sin(x);
fplot(f, [6 9]);

Matt J on 20 Mar 2020
Edited: Matt J on 20 Mar 2020
You can assign NaN to anything you don't want plotted. Example,
x=linspace(0,2,1000);
f=sin(x);
f( 0.5<=x & x<=1)=nan;
plot(x,f);

R2019b

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