420 lines
9.8 KiB
Python
420 lines
9.8 KiB
Python
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"""Curves in 2-dimensional Euclidean space.
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Contains
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========
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Curve
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"""
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from sympy import sqrt
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from sympy.core import sympify, diff
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from sympy.core.compatibility import is_sequence
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from sympy.core.containers import Tuple
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from sympy.core.symbol import _symbol
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from sympy.geometry.entity import GeometryEntity, GeometrySet
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from sympy.geometry.point import Point
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from sympy.integrals import integrate
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class Curve(GeometrySet):
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"""A curve in space.
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A curve is defined by parametric functions for the coordinates, a
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parameter and the lower and upper bounds for the parameter value.
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Parameters
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==========
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function : list of functions
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limits : 3-tuple
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Function parameter and lower and upper bounds.
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Attributes
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==========
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functions
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parameter
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limits
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Raises
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======
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ValueError
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When `functions` are specified incorrectly.
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When `limits` are specified incorrectly.
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Examples
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========
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>>> from sympy import sin, cos, interpolate
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>>> from sympy.abc import t, a
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>>> from sympy.geometry import Curve
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>>> C = Curve((sin(t), cos(t)), (t, 0, 2))
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>>> C.functions
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(sin(t), cos(t))
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>>> C.limits
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(t, 0, 2)
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>>> C.parameter
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t
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>>> C = Curve((t, interpolate([1, 4, 9, 16], t)), (t, 0, 1)); C
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Curve((t, t**2), (t, 0, 1))
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>>> C.subs(t, 4)
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Point2D(4, 16)
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>>> C.arbitrary_point(a)
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Point2D(a, a**2)
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See Also
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========
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sympy.core.function.Function
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sympy.polys.polyfuncs.interpolate
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"""
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def __new__(cls, function, limits):
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fun = sympify(function)
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if not is_sequence(fun) or len(fun) != 2:
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raise ValueError("Function argument should be (x(t), y(t)) "
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"but got %s" % str(function))
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if not is_sequence(limits) or len(limits) != 3:
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raise ValueError("Limit argument should be (t, tmin, tmax) "
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"but got %s" % str(limits))
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return GeometryEntity.__new__(cls, Tuple(*fun), Tuple(*limits))
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def __call__(self, f):
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return self.subs(self.parameter, f)
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def _eval_subs(self, old, new):
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if old == self.parameter:
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return Point(*[f.subs(old, new) for f in self.functions])
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def arbitrary_point(self, parameter='t'):
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"""A parameterized point on the curve.
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Parameters
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==========
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parameter : str or Symbol, optional
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Default value is 't'.
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The Curve's parameter is selected with None or self.parameter
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otherwise the provided symbol is used.
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Returns
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=======
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Point :
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Returns a point in parametric form.
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Raises
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======
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ValueError
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When `parameter` already appears in the functions.
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Examples
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========
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>>> from sympy import Symbol
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>>> from sympy.abc import s
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>>> from sympy.geometry import Curve
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>>> C = Curve([2*s, s**2], (s, 0, 2))
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>>> C.arbitrary_point()
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Point2D(2*t, t**2)
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>>> C.arbitrary_point(C.parameter)
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Point2D(2*s, s**2)
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>>> C.arbitrary_point(None)
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Point2D(2*s, s**2)
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>>> C.arbitrary_point(Symbol('a'))
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Point2D(2*a, a**2)
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See Also
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========
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sympy.geometry.point.Point
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"""
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if parameter is None:
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return Point(*self.functions)
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tnew = _symbol(parameter, self.parameter, real=True)
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t = self.parameter
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if (tnew.name != t.name and
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tnew.name in (f.name for f in self.free_symbols)):
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raise ValueError('Symbol %s already appears in object '
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'and cannot be used as a parameter.' % tnew.name)
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return Point(*[w.subs(t, tnew) for w in self.functions])
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@property
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def free_symbols(self):
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"""Return a set of symbols other than the bound symbols used to
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parametrically define the Curve.
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Returns
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=======
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set :
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Set of all non-parameterized symbols.
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Examples
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========
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>>> from sympy.abc import t, a
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>>> from sympy.geometry import Curve
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>>> Curve((t, t**2), (t, 0, 2)).free_symbols
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set()
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>>> Curve((t, t**2), (t, a, 2)).free_symbols
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{a}
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"""
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free = set()
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for a in self.functions + self.limits[1:]:
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free |= a.free_symbols
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free = free.difference({self.parameter})
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return free
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@property
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def ambient_dimension(self):
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"""The dimension of the curve.
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Returns
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=======
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int :
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the dimension of curve.
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Examples
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========
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>>> from sympy.abc import t
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>>> from sympy.geometry import Curve
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>>> C = Curve((t, t**2), (t, 0, 2))
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>>> C.ambient_dimension
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2
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"""
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return len(self.args[0])
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@property
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def functions(self):
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"""The functions specifying the curve.
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Returns
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=======
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functions :
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list of parameterized coordinate functions.
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Examples
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========
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>>> from sympy.abc import t
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>>> from sympy.geometry import Curve
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>>> C = Curve((t, t**2), (t, 0, 2))
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>>> C.functions
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(t, t**2)
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See Also
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========
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parameter
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"""
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return self.args[0]
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@property
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def limits(self):
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"""The limits for the curve.
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Returns
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=======
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limits : tuple
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Contains parameter and lower and upper limits.
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Examples
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========
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>>> from sympy.abc import t
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>>> from sympy.geometry import Curve
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>>> C = Curve([t, t**3], (t, -2, 2))
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>>> C.limits
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(t, -2, 2)
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See Also
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========
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plot_interval
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"""
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return self.args[1]
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@property
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def parameter(self):
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"""The curve function variable.
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Returns
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=======
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Symbol :
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returns a bound symbol.
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Examples
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========
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>>> from sympy.abc import t
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>>> from sympy.geometry import Curve
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>>> C = Curve([t, t**2], (t, 0, 2))
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>>> C.parameter
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t
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See Also
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========
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functions
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"""
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return self.args[1][0]
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@property
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def length(self):
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"""The curve length.
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Examples
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========
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>>> from sympy.geometry.curve import Curve
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>>> from sympy.abc import t
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>>> Curve((t, t), (t, 0, 1)).length
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sqrt(2)
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"""
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integrand = sqrt(sum(diff(func, self.limits[0])**2 for func in self.functions))
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return integrate(integrand, self.limits)
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def plot_interval(self, parameter='t'):
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"""The plot interval for the default geometric plot of the curve.
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Parameters
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==========
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parameter : str or Symbol, optional
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Default value is 't';
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otherwise the provided symbol is used.
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Returns
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=======
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List :
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the plot interval as below:
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[parameter, lower_bound, upper_bound]
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Examples
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========
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>>> from sympy import Curve, sin
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>>> from sympy.abc import x, s
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>>> Curve((x, sin(x)), (x, 1, 2)).plot_interval()
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[t, 1, 2]
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>>> Curve((x, sin(x)), (x, 1, 2)).plot_interval(s)
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[s, 1, 2]
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See Also
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========
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limits : Returns limits of the parameter interval
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"""
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t = _symbol(parameter, self.parameter, real=True)
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return [t] + list(self.limits[1:])
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def rotate(self, angle=0, pt=None):
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"""This function is used to rotate a curve along given point ``pt`` at given angle(in radian).
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Parameters
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==========
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angle :
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the angle at which the curve will be rotated(in radian) in counterclockwise direction.
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default value of angle is 0.
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pt : Point
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the point along which the curve will be rotated.
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If no point given, the curve will be rotated around origin.
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Returns
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=======
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Curve :
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returns a curve rotated at given angle along given point.
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Examples
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========
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>>> from sympy.geometry.curve import Curve
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>>> from sympy.abc import x
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>>> from sympy import pi
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>>> Curve((x, x), (x, 0, 1)).rotate(pi/2)
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Curve((-x, x), (x, 0, 1))
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"""
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from sympy.matrices import Matrix, rot_axis3
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if pt:
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pt = -Point(pt, dim=2)
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else:
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pt = Point(0,0)
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rv = self.translate(*pt.args)
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f = list(rv.functions)
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f.append(0)
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f = Matrix(1, 3, f)
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f *= rot_axis3(angle)
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rv = self.func(f[0, :2].tolist()[0], self.limits)
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pt = -pt
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return rv.translate(*pt.args)
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def scale(self, x=1, y=1, pt=None):
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"""Override GeometryEntity.scale since Curve is not made up of Points.
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Returns
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=======
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Curve :
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returns scaled curve.
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Examples
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========
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>>> from sympy.geometry.curve import Curve
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>>> from sympy.abc import x
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>>> Curve((x, x), (x, 0, 1)).scale(2)
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Curve((2*x, x), (x, 0, 1))
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"""
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if pt:
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pt = Point(pt, dim=2)
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return self.translate(*(-pt).args).scale(x, y).translate(*pt.args)
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fx, fy = self.functions
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return self.func((fx*x, fy*y), self.limits)
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def translate(self, x=0, y=0):
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"""Translate the Curve by (x, y).
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Returns
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=======
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Curve :
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returns a translated curve.
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Examples
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========
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>>> from sympy.geometry.curve import Curve
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>>> from sympy.abc import x
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>>> Curve((x, x), (x, 0, 1)).translate(1, 2)
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Curve((x + 1, x + 2), (x, 0, 1))
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"""
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fx, fy = self.functions
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return self.func((fx + x, fy + y), self.limits)
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