0 个投票

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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Thorsten
Thorsten 2015-5-26
编辑：Thorsten 2015-5-26

0 个投票

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)

更多回答（2 个）

Jos (10584)
Jos (10584) 2015-5-26

0 个投票

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)
Titus Edelhofer
Titus Edelhofer 2015-5-26

0 个投票

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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