Plotting 1/x correctly
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Lasse Sivertsen
on 26 May 2015
Answered: Titus Edelhofer
on 26 May 2015
I'm trying to plot a simple function, 1/x. However it does not seem to work as intended. I define a linspace for my variable x and then use the plot() function.
As seen in the picture, for X=3, Y= 4.95. How is this possible? For X=3, Y should be equal to 0.33?
Is there something I'm missing causing the function to break the laws of mathematics? Changing the linspace size, or simply step size results in large differences as well.
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Accepted Answer
Thorsten
on 26 May 2015
Edited: Thorsten
on 26 May 2015
Because you have not specified the x values in your plot, they run from 1 to the numel(s). So X is not an absolute value but the index into your x, defined as
x = linspace(0, 10, 100);
Then
x(3) = 0.2020
so y = 1/x = 4.95.
To get the right values, use
plot(x, 1./x)
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More Answers (2)
Jos (10584)
on 26 May 2015
Your plotting values against their index. And indeed, since x(3) is not equal to 3, but 0.2020, y(3) is not 1/3. You can use plot(x,1/.x)
Try this:
x = linspace(0,10,100) ;
y = 1./x ;
plot(x, y)
idx = 3, x(idx), y(idx)
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Titus Edelhofer
on 26 May 2015
Adding to Thorsten's answer: you need to put x on the x axis while plotting:
plot(x, 1./x);
Titus
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