Sympy yields `TypeError: unsupported operand type(s) for *: 'interval' and 'complex'` for complex rational expression

Question

I have this sympy script:

from sympy import *
from sympy.plotting import plot_implicit

x, y = symbols('x y', real=True)

alpha = sqrt(2) / 2
expr = 1 + ((1-alpha) * x + y*I) / (1 - alpha * (x + y*I))**2

expr = Eq(abs(expr), 1)
p1 = plot_implicit(expr)

Which is trying to solve R(z) = 1 where:

As far as I can tell the expression I am giving it is correct. Why am I getting incompatible types? Note that if I get rid of the denominator I do get a plot.

Full error:

Traceback (most recent call last):
  File "/home/makogan/Documents/University/Math521/A3/A5.py", line 49, in <module>
    p1 = plot_implicit(expr)
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot_implicit.py", line 430, in plot_implicit
    p.show()
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot.py", line 240, in show
    self._backend.show()
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot.py", line 1533, in show
    self.process_series()
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot.py", line 1530, in process_series
    self._process_series(series, ax, parent)
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot.py", line 1398, in _process_series
    points = s.get_raster()
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/plot_implicit.py", line 87, in get_raster
    func(xinterval, yinterval)
  File "/home/makogan/.local/lib/python3.10/site-packages/sympy/plotting/experimental_lambdify.py", line 272, in __call__
    return self.lambda_func(*args, **kwargs)
  File "<string>", line 1, in <lambda>
TypeError: unsupported operand type(s) for *: 'interval' and 'complex'

Asked By: Makogan

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Source

Answer 1

That’s caused by the fact that sympy’s plotting module is using an old and obsolete evaluation module. If you try this new plotting module you’ll get the answer:

from sympy import *
from spb import *
var("x:z")

x, y = symbols('x y', real=True)

alpha = sqrt(2) / 2
expr = 1 + ((1 - alpha) * z) / (1 - alpha * z)**2
expr = expr.subs(z, x + I*y)

expr = Eq(abs(expr), 1)
p1 = plot_implicit(expr, x)

Answered By: Davide_sd

Sympy yields `TypeError: unsupported operand type(s) for *: 'interval' and 'complex'` for complex rational expression

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