How to remove the horizontal streamline when plotting contour using atan2? Streamline plotting help

Hi. I have a streamline plot as follow:

[X,Y] = meshgrid (-2:0.01:2,-2:0.01:2);

Z =atan2(Y,X) +Y;

contour (X,Y,Z, 30);

However as you can see there exists that one one horizontal streamline in the middle from (-2,0) to (0,0) that shouldn't be there. Any ideas how i can remove it or what i should change?

I will greatly appreciate any help provided. Thank you!

Answer 1

[Massimo Zanetti]

Why they shouldn't be there? They SHOULD be there. This is the plot of the atan2 function:

That, you can easily get following the help page of atan2:

[X,Y] = meshgrid(-4:0.1:4,-4:0.1:4);
P = atan2(Y,X);
surf(X,Y,P);
view(45,45);

The function is discontinuous at Y=0 for all X<0.