Plotting 1/x correctly

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.

Answer 1

[Thorsten]

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)

Answer 2

[Jos (10584)]

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)

Answer 3

[Titus Edelhofer]

Adding to Thorsten's answer: you need to put x on the x axis while plotting:

plot(x, 1./x);

Titus