ADALINE with 2 features decision function. Chapter 2, Page 40

[manas007]

Hello,
While plotting the decision boundary with just 2 features for ADALINE, the decision class function is simply
w1 ∗ x1 + w2 ∗ x2 + b = 0

and therefore in simple slope intercept form, x2 can be simplified to
x2 = (−w1/w2) ∗ x1 − (b/w2)

when I plot this, the line does not separate the two classes. I posted the question on cross-validated exchange as well and the answer was to label y as {-1,1} instead of {0,1} and indeed the plot works correctly. I am wondering why is this?

Link to question

[manas007]

@rasbt is there an explanation why the labels should be {-1,1} instead of {0,1} ? The above plot works when labels are {-1,1} but not when labels are {0,1}. This is not explained in the book and therefore is confusing when drawing the boundary using the simple line equation instead of the meshgrid.