Code style changes

lti.py

------

LTI is an abstract class? Needs __call__ abc method

Spaces between function defs

class LTI docstring their timebases much match

phaseplot.py

------------

Remove semi-colons

| Function | Purpose |

|---|---|

| `bode` | Compute the magnitude and phase of the frequency response

| `bodeplot` | Create a Bode plot of the system

| `freqresp` | Evaluate the frequency response of a linear system |

| `gangoffourplot` | Gang-of-Four plot

| `margin` | returns frequencies for gain margins, gain margins, frequencies for phase margins, phase margins

| `marginplot` | Plot all the amplitude and phase margins of the system |

| `nicholsplot` | Create a Nichols plot of the system |

| `nyquist` | Compute the real and imaginary parts of the frequency response |

| `nyquistplot` | Create a Nyquist plot of the system |

| `pzmap` | Create a pole-zero map of the system |

| `rlocus` | Computes and plots the root locus of the SISO LTISystem (deprecated) |

| `rlocusplot` | Computes and plots the root locus of the SISO LTISystem |

| `sigma` | Compute the singular values sv of the frequency response |

| `sigmaplot` | Plot the singular values of the frequency response of the system |

Correspondence table

| Julia | Python-Control current | Proposal |

|---|---|---|

| `mag, phase, w = bode(sys)` | `mag, phase, w = bode_plot(sys, plot=False)` | `fr = freqresp(sys)` |

| `fr = freqresp(sys, w)` | `mag, phase, w = control.matlab.freqresp(sys, w)` | `fr = freqresp(sys, w)` |

| n/a | n/a | `fr.plot()` |

| `bodeplot(sys)` | `bode_plot(sys)` | no change |

| `fig = bodeplot(sys)` | n/a | `fig, axes = bode_plot(sys)` |

| `gangoffourplot(P, C)` | `gangof4_plot(P, C)` | no change |

| `fig = gangoffourplot(P, C)` | n/a | `fig, axes = gangof4_plot(P, C)` |

| `ωgm, gm, ωpm, pm = margin(sys)` | `gm, pm, wg, wp = margin(sys)` | no change |

| `marginplot(sys)` | n/a | no change for now |

| `nicholsplot(sys)` | `nichols_plot(sys)` | no change |

| `fig = nicholsplot(sys)` | n/a | `ax = nichols_plot(sys)` |

| n/a | n/a | `nichols_plot(sys, ax=ax)` |

| `re, im, w = nyquist(sys)` | n/a | no change for now |

| `nyquistplot(sys)` | `nyquist_plot(sys)` | no change |

| `fig = nyquistplot(sys)` | n/a | `ax = nyquist_plot(sys)` |

| n/a | n/a | `nyquist_plot(sys, ax=ax)` |

| `p, z = pole(sys), tzero(sys)` | `p, z = pzmap(sys, plot=False)` | `p, z = pole(sys), zero(sys)` |

| `pzmap(sys)` | `pzmap(sys)` | no change |

| `fig = pzmap(fig, sys)` | n/a | `ax = pzmap(sys)` |

| n/a | n/a | `pzmap(sys, ax=ax)` |

| n/a | `roots, k_out = root_locus(sys, plot=None)` | `roots, k_out = root_locus(sys)` |

| `rlocusplot(sys)` | `root_locus(sys)` | `root_locus_plot(sys)` |

| n/a | n/a | `ax = root_locus_plot(sys)` |

| n/a | n/a | `root_locus_plot(sys, ax=ax)` |

| `sv, w = sigma(sys)` | `sigma, w = singular_values_plot(sys, plot=False)` | `sigma, w = singular_values(sys)` |

| `sigmaplot(sys)` | `singular_values_plot(sys)` | no change |

| n/a | n/a | `ax = singular_values_plot(sys)` |

| n/a | n/a | `singular_values_plot(ax=ax)` |

| `y, t, x = step(sys)` | `T, yout = step_response(sys)` | `response = step_response(sys)`* |

| `y, t, x = impulse(sys)` | `T, yout = impulse_response(sys)` | `response = impulse_response(sys)`* |

| `y, t, x = lsim(sys, u, t)` | `T, yout = forced_response(sys, T, u)` | `response = forced_response(sys, T, u)`* |

| `Plots.plot(t, y)` | `plt.plot(T, yout)` | `response.plot()`* |

| n/a | n/a | `ax = response.plot()`* |

| n/a | n/a | `response.plot(ax=ax)`* |

\* - these changes are part of a different pull request by Richard.

This will affect the following plotting functions

* root_locus

* pzmap

* bode_plot

* nyquist_plot

* gangof4_plot

* nichols_plot

* sisotool

G1 = tf([2, 2], [1, 0, -1])

root_locus_plot(G1) # previously named root_locus

G1 = tf([2, 2], [1, 0, -1])

root_locus_plot(G1)