plot in piecewise regression

[kcrisman]

P = piecewise([((0,2),x),((2,6),2)])
print P
plot(P)

Before this would have plotted the whole thing, now it defaults to the usual plotting only from -1 to 1 (which of course gives an error).

Moreover pieces are joined and detect_poles=True option skips the origin for no good reason:

P = piecewise([((-1,2),x),((2,5),1)])
print P
plot(P, -1, 5, detect_poles=True)

CC: @paulmasson

Component: symbolics

Branch/Commit: u/rws/21618-1 @ c008c29

Issue created by migration from https://trac.sagemath.org/ticket/21618

[paulmasson]

comment:2

The old Piecewise has a custom plot method. This method is omitted in the current piecewise.

[kcrisman]

comment:3

Correct. So it would be nice to emulate that so everyone's code doesn't break - I had a not-so-nice time drawing graphs on the fly in class today because of this. It seems reasonable, since piecewise is an unusual situation.

[rwst]

Branch: u/rws/plot_in_piecewise_regression

[rwst]

comment:5

Oops I just saw the second complaint. This will not be as easy.

---

New commits:

c98505b

21618: plotting piecewise without need of giving domain interval

[rwst]

Commit: c98505b

[rwst]

comment:7

Note that your command plot(P, -1, 5, detect_poles=True) also does not work on Sage-7.1, i.e., the old piecewise, and plot(P, detect_poles=True) also has a gap at x=0. So, this particularly is rather an enhancement of plot, not a bug in piecewise.

[rwst]

Changed branch from u/rws/plot_in_piecewise_regression to u/rws/21618-1

[rwst]

New commits:

c008c29

21618: plotting piecewise without need of giving domain interval

[rwst]

Changed commit from c98505b to c008c29

[novoselt]

comment:10

1. Why there is commented code? Reference to some ticket explaining stuff is fine, but not strange imports etc.
2. Why there is extra printing of pieces???
3. If I do specify the domain, then each piece is plotted over this domain!

I'll see if I can resolve all this in the next hour or so.

[novoselt]

comment:11

Address 1&2 and simplify a bit to get

        def plot(cls, self, parameters, variable, *args, **kwds):
            from sage.plot.all import plot, Graphics
            g = Graphics()
            for (dom, fun) in self.items():
                g += plot(fun, (variable, dom.inf(), dom.sup()), *args, **kwds)
                # If it's the first piece, pass all arguments. Otherwise,
                # filter out 'legend_label' so that we don't add each
                # piece to the legend separately (trac #12651).
                kwds.pop('legend_label', None)
            return g

3 is tricky, however, because of a variety of ways to pass left and right bounds. I think we should factor out the logic of getting these bounds into a separate function which will say always set xmin/xmax keywords, then we can call this function in the top level plot as well as plot methods and have a guaranteed uniform behavior. Thoughts?

There is also
4. No documentation and examples at all!!!

[rwst]

comment:12

Andrey, please go ahead with your own branch, the plotting code is quite opaque and uninteresting to me, and I'm into other projects right now.

[kcrisman]

When fixing this (if ever), we should check whether #11225 is also resolved at the same time (which is likely).