how to solve this

[Torsten]

How to solve what ?

Answer 1

[John D'Errico]

You already solved it. So where is the problem? If I had to guess, it is why the circle you just plotted does not appear circular. For that, you need to learn why it is that you use

axis equal

Which forces the x and y axes to have the same spacing.

Or, maybe why it is that the variables x and y you defined before the call to ezplot have nothing to do with the plot you show, so no impact. That is because ezplot does not use workspace variables.

But maybe your question is something completely different.

[daniel]

How do I change the ranges of x and y according to the image

[John D'Errico]

You probably want to use xlim and ylim. For example, I'll use ezplot, since you did already. (fimplicit or fplot are better (newer) tools though.)

ezplot('x.^2 +x.*y + y.^2 - 3')

By default, ezplot decided to use axes that go to [-6,+6] on each axis. You can change that in several ways.

For example, let me redo the plot, but this time, I'll use xlim and ylim.

ezplot('x.^2 +x.*y + y.^2 - 3')
xlim([-4,4])
ylim([-3,3])

Or, you can use handle graphics calls to modify the plot.

ezplot('x.^2 +x.*y + y.^2 - 3')

The axis handle allows you to change any of those axis properties after the plot was created. It is found by a call to gca.

gca

ans = 
  Axes ({x}^{2} +{x} {y} + {y}^{2} - {3} = {0}) with properties:

             XLim: [-6.2832 6.2832]
             YLim: [-6.2832 6.2832]
           XScale: 'linear'
           YScale: 'linear'
    GridLineStyle: '-'
         Position: [0.1300 0.1100 0.7750 0.8150]
            Units: 'normalized'

  Show all properties

And now we can modify any of those properties.

set(gca,'XLim',[-5,5],'YLim',[-5,5])