Hello all,
Should generate_plot_points() be modified to log-sample on plots where the
x scale is logarithmic? I'd be willing to write the patch up but I'd like
to know that it would be desired behavior before I do so.
I've been using sage to graph the frequency responses of a couple of
filters. While I was generating the plots, the results sage generated by
default were not correct - sage had picked too few sample points.
Increasing the number of points by an order of magnitude worked, but it
significantly slowed generation of the figures, which was undesirable as I
was looking to make them interactive. Restating the function in terms of x
<- 2^x and changing the axes appropriately solved the problem.
I think plot() should 'just work' the way one would intuitively expect.
However, I don't know - there may be (/probably are) use cases where this
would be far from expected behavior.
Code, to illustrate:
def mag2db(x):
return 20*log(x, 10)
def plot_tf(tf, cutoff, var, domain=(1, 1e6), thresh=1e-2, **kwargs):
tf = tf.substitute({var:var*i})
return plot_semilogx(mag2db(abs(tf)), (var, domain[0], domain[1]), base=
2, **kwargs)
def plot_tf_log(tf, cutoff, var, domain=(1, 1e6), thresh=1e-2, **kwargs):
tf = tf.substitute({var:2^(var)*i})
return plot(mag2db(abs(tf)), (var, log(domain[0], 2), log(domain[1], 2
)), **kwargs)
@interact
def _(w=slider(0, 20000, step_size=500, default=2000, label='$\\omega_c$'),
R=slider(0, 5, default=1, step_size=0.2), C=slider(0, 10, default=1,
step_size=0.2)):
l = L.substitute(omega_c=w, r=R, c=C)
b = B.substitute(omega_c=w, r=R, c=C)
h = H.substitute(omega_c=w, r=R, c=C)
p = plot_tf(l, w, s, color='blue')
p += plot_tf(b, w, s, color='red')
p += plot_tf(h, w, s, color='green')
p.show(ymin=-30, ymax=5)
p2 = plot_tf_log(l, w, s, color='blue')
p2 += plot_tf_log(b, w, s, color='red')
p2 += plot_tf_log(h, w, s, color='green')
p2.show(ymin=-30, ymax=5)
print(l) # 4000000/(s^2 + 4000*s + 4000000)
print(b) # 2000*s/(s^2 + 4000*s + 4000000)
print(h) # s^2/(s^2 + 4000.00000000000*s + 4000000)
[image: a.png] <about:invalid#zClosurez>[image: b.png]
Thanks,
Blair Mason
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