Implicit matplotlib python graphs

Good time of day!

There is a function of two variables (the decision function):

def dec_func(self, x, y):
    res = 0
    for i, w in enumerate(self.W):
        res += w * self.F[i](Point(x, y))
    return res

We need to plot this function when res = 0. That is, we need to get y from the list X for each x, so that when the function is executed, the result is 0.

UPD:

There is an implemented function that, given X, can get approximately correct Y (with a certain accuracy):

def plot_data(self, start=-15, end=15, step=1):
    X = [i for i in range(start, end, step)]
    Y = []
    x_to_remove = []
    for x in X:
        k = 0
        y_old = 0
        step = 0.05
        old_res = self.dec_func(x, y_old)
        while abs(old_res) > 0.01:
            if k > 3000:
                break
            k += 1
            y = y_old + step
            res = self.dec_func(x, y)
            if abs(old_res) > abs(res):
                y_old = y
                step *= 1.2
            else:
                y_old = y
                step = -step / 2
            old_res = res
        if k > 3000:
            print(y_old, x, old_res)
            x_to_remove.append(x)
        else:
            Y.append(y_old)
    for x in x_to_remove:
        X.remove(x)
    return X, Y

But the problem is that this implementation does not allow get multiple y values for a single x.