Poly1d with Matplotlib

Question

I'm trying to plot a function which is an object of numpy.poly1d. In my case it is y = -x^2 + 7x -7. So now I'm trying to plot it like a nice parabola, however when I plot it, it looks like this:

So I wondered if anybody could tell me how to make this line smooth.

This is my code:

t = np.poly1d([-1, 7, -7])

plt.plot(t)
plt.show()

Answer 1

np.poly1d() creates a polynomial. If you plot that, you only get its coefficient values, of which you have 3. So effectively you plot the values -1, 7 and -7.

You want to pass some x values to your polynomial to get the corresponding y values.

p = np.poly1d([-1, 7, -7])
x = np.arange(20)
y = p(x)
plt.plot(x, y)
plt.show()