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

[novoselt]

Description changed:

--- 
+++ 
@@ -5,3 +5,11 @@
 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)
+```

[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.