x, y = [1.,2.,3.], [2.,4.,6.]
weight = 0.0
losses = []
for _ in range(60):
    residuals = [weight*a-b for a,b in zip(x,y,strict=True)]
    losses.append(sum(r*r for r in residuals)/len(x))
    gradient = 2*sum(r*a for r,a in zip(residuals,x,strict=True))/len(x)
    weight -= 0.05*gradient
print(f"weight: {weight:.3f}")
print("loss decreased:", losses[-1] < losses[0])