implicit_plot totally sucks when input an equation

[williamstein]

Make Sage hurt:

var('x,y')
implicit_plot(x^2+y^2 == 1, (x,-2,2), (y,-2,2))

The problem is that implicit_plot takes a function, not a symbolic equation, so it views "x^2+y2 == 1" as a function --- and that is very painful.

SOLUTION: Check if the input is an equation, and if so, make RHS zero, and plot corresponding function equal to 0.

Component: graphics

Issue created by migration from https://trac.sagemath.org/ticket/5706

[williamstein]

comment:1

Attachment: trac_5706.patch.gz

[sagetrac-mabshoff]

comment:2

There is one doctest failure in here:

sage -t -long "devel/sage/sage/plot/contour_plot.py"
**********************************************************************
File "/scratch/mabshoff/sage-3.4.1.rc2/devel/sage/sage/plot/contour_plot.py", line 195:
    sage: implicit_plot(x^2+y^2 == 2, (-3,3), (-3,3)).show(aspect_ratio=1)
Expected nothing
Got:
    doctest:2846: DeprecationWarning: Substitution using function-call syntax and 
unnamed arguments is deprecated and will be removed from a future release of Sage; you 
can use named arguments instead, like EXPR(x=..., y=...)
**********************************************************************
1 items had failures:

Cheers,

Michael

[sagetrac-mabshoff]

Attachment: trac_5706.2.patch.gz

Slightly fixed up version of William's patch due to deprecation of substitution (see #5413)

[sagetrac-mabshoff]

comment:3

Merged trac_5706.2.patch in Sage 3.4.1.rc2.

Cheers,

Michael

[sagetrac-mabshoff]

comment:4

Ooops, didn't change the review status.

Cheers,

Michael