Why does matlab scale x-axis automatically

Hello,

Why does Matlab scale x axis automatically when it is a decimal number?

For example,

plot(sin([0:0.01:2*pi]))

This graph is not what I asked to plot! The x-axis starts from 0 to 700, when it should be 0 to 7.

At least the x-axis should have shown that it is *10^-2, but it doesn't.

This is misleading, sin(100) isn't 0.8415!

why does MatLab scale all decimal places automatically like this?

And how do I make Matlab to show correct x-axis?

[Adam]

It is exactly what you asked it to plot, you just didn't ask it what you thought you had! There is no auto-scaling going on.

Answer 1

[Adam]

plot( x, y )

plots the values you want on the x axis.

plot( y )

as you have done just defaults to using indices along the x axis so there are 600 and whatever elements in your array and you get that many elements in x in your plot.

doc plot

explains the syntax.

x = 0:0.01:2*pi;
y = sin( x );
plot(x, y)

should work fine by simply telling it what you want to plot as x and what you want to plot as y.

[Steven Lord]

Adam is correct. There's no scaling of X coordinates taking place. The specific syntax in the Description section of the plot documentation page that covers this case is:

plot(Y) creates a 2-D line plot of the data in Y versus the index of each value.

• If Y is a vector, then the x-axis scale ranges from 1 to length(Y).

Call plot with two inputs, as Adam showed.