plot_implicit behavior

[Amit Saha]

Hello,

Consider the following program:

"""
Draw a line given two points it passes through
"""

from sympy import Point, Line, plot_implicit

def draw_line(x1, y1, x2, y2):

p1 = Point(x1, y1)
p2 = Point(x2, y2)
l = Line(p1, p2)
eqn = l.equation()
print(eqn)
plot_implicit(eqn)

if __name__=='__main__':
x1, y1 = -1, 0
x2, y2 = 2, 3
draw_line(x1, y1, x2, y2)

Basically, I am creating a line object passing through (-1,0) and
(2,3). When I use plot_implicit() to draw the this line, it randomly
draws a line passing through (0, -1) and (3,2) instead about 40% of
the times.

What could be happening here?

Thanks for any hints.

Best,
Amit.

[Amit Saha]

Can someone please try this and see if this is indeed the case or I am
seeing something really weird?

Thanks!
-Amit.



--
http://echorand.me

[Aaron Meurer]

I can reproduce it. It's definitely a bug. I'm guessing plot_implicit doesn't have a well-defined way of choosing which variable is x and which variable is y.

Aaron Meurer

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[Amit Saha]

On Tue, Apr 15, 2014 at 2:43 AM, Aaron Meurer <asme...@gmail.com> wrote:
> I can reproduce it. It's definitely a bug. I'm guessing plot_implicit
> doesn't have a well-defined way of choosing which variable is x and which
> variable is y.

That indeed is the case. I thought of a fairly straightforward method:
https://github.com/sympy/sympy/pull/7419

I am keen to work towards fixing this, so comments appreciated.

Best,
Amit.