Complex Interpolation

AUTHORS:

  • Ethan Van Andel (2009): initial version

Development supported by NSF award No. 0702939.

class sage.calculus.interpolators.CCSpline[source]

Bases: object

A CCSpline object contains a cubic interpolation of a figure in the complex plane.

EXAMPLES:

A simple square:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: cs = complex_cubic_spline(pts)
sage: cs.value(0)
(-1-1j)
sage: cs.derivative(0)
(0.9549296...-0.9549296...j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> cs = complex_cubic_spline(pts)
>>> cs.value(Integer(0))
(-1-1j)
>>> cs.derivative(Integer(0))
(0.9549296...-0.9549296...j)
derivative(t)[source]

Return the derivative (speed and direction of the curve) of a given point from the parameter t.

INPUT:

  • t – double; the parameter value for the parameterized curve, between 0 and 2*pi

OUTPUT:

A complex number representing the derivative at the point on the figure corresponding to the input t.

EXAMPLES:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: cs = complex_cubic_spline(pts)
sage: cs.derivative(3 / 5)
(1.40578892327...-0.225417136326...j)
sage: from math import pi
sage: cs.derivative(0) - cs.derivative(2 * pi)
0j
sage: cs.derivative(-6)
(2.52047692949...-1.89392588310...j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> cs = complex_cubic_spline(pts)
>>> cs.derivative(Integer(3) / Integer(5))
(1.40578892327...-0.225417136326...j)
>>> from math import pi
>>> cs.derivative(Integer(0)) - cs.derivative(Integer(2) * pi)
0j
>>> cs.derivative(-Integer(6))
(2.52047692949...-1.89392588310...j)
value(t)[source]

Return the location of a given point from the parameter t.

INPUT:

  • t – double; the parameter value for the parameterized curve, between 0 and 2*pi

OUTPUT:

A complex number representing the point on the figure corresponding to the input t.

EXAMPLES:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: cs = complex_cubic_spline(pts)
sage: cs.value(4 / 7)
(-0.303961332787...-1.34716728183...j)
sage: from math import pi
sage: cs.value(0) - cs.value(2*pi)
0j
sage: cs.value(-2.73452)
(0.934561222231...+0.881366116402...j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> cs = complex_cubic_spline(pts)
>>> cs.value(Integer(4) / Integer(7))
(-0.303961332787...-1.34716728183...j)
>>> from math import pi
>>> cs.value(Integer(0)) - cs.value(Integer(2)*pi)
0j
>>> cs.value(-RealNumber('2.73452'))
(0.934561222231...+0.881366116402...j)
class sage.calculus.interpolators.PSpline[source]

Bases: object

A CCSpline object contains a polygon interpolation of a figure in the complex plane.

EXAMPLES:

A simple square:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: ps = polygon_spline(pts)
sage: ps.value(0)
(-1-1j)
sage: ps.derivative(0)
(1.27323954...+0j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> ps = polygon_spline(pts)
>>> ps.value(Integer(0))
(-1-1j)
>>> ps.derivative(Integer(0))
(1.27323954...+0j)
derivative(t)[source]

Return the derivative (speed and direction of the curve) of a given point from the parameter t.

INPUT:

  • t – double; the parameter value for the parameterized curve, between 0 and 2*pi

OUTPUT:

A complex number representing the derivative at the point on the polygon corresponding to the input t.

EXAMPLES:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: ps = polygon_spline(pts)
sage: ps.derivative(1 / 3)
(1.27323954473...+0j)
sage: from math import pi
sage: ps.derivative(0) - ps.derivative(2*pi)
0j
sage: ps.derivative(10)
(-1.27323954473...+0j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> ps = polygon_spline(pts)
>>> ps.derivative(Integer(1) / Integer(3))
(1.27323954473...+0j)
>>> from math import pi
>>> ps.derivative(Integer(0)) - ps.derivative(Integer(2)*pi)
0j
>>> ps.derivative(Integer(10))
(-1.27323954473...+0j)
value(t)[source]

Return the derivative (speed and direction of the curve) of a given point from the parameter t.

INPUT:

  • t – double; the parameter value for the parameterized curve, between 0 and 2*pi

OUTPUT:

A complex number representing the point on the polygon corresponding to the input t.

EXAMPLES:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: ps = polygon_spline(pts)
sage: ps.value(.5)
(-0.363380227632...-1j)
sage: ps.value(0) - ps.value(2*RDF.pi())
0j
sage: ps.value(10)
(0.26760455264...+1j)

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> ps = polygon_spline(pts)
>>> ps.value(RealNumber('.5'))
(-0.363380227632...-1j)
>>> ps.value(Integer(0)) - ps.value(Integer(2)*RDF.pi())
0j
>>> ps.value(Integer(10))
(0.26760455264...+1j)
sage.calculus.interpolators.complex_cubic_spline(pts)[source]

Create a cubic spline interpolated figure from a set of complex or \((x,y)\) points. The figure will be a parametric curve from 0 to 2*pi. The returned values will be complex, not \((x,y)\).

INPUT:

  • pts – list or array of complex numbers, or tuples of the form \((x,y)\)

EXAMPLES:

A simple square:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: cs = complex_cubic_spline(pts)
sage: fx = lambda x: cs.value(x).real
sage: fy = lambda x: cs.value(x).imag
sage: from math import pi
sage: show(parametric_plot((fx, fy), (0, 2*pi)))                                # needs sage.plot
sage: m = Riemann_Map([lambda x: cs.value(real(x))],
....:                 [lambda x: cs.derivative(real(x))], 0)
sage: show(m.plot_colored() + m.plot_spiderweb())                               # needs sage.plot

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> cs = complex_cubic_spline(pts)
>>> fx = lambda x: cs.value(x).real
>>> fy = lambda x: cs.value(x).imag
>>> from math import pi
>>> show(parametric_plot((fx, fy), (Integer(0), Integer(2)*pi)))                                # needs sage.plot
>>> m = Riemann_Map([lambda x: cs.value(real(x))],
...                 [lambda x: cs.derivative(real(x))], Integer(0))
>>> show(m.plot_colored() + m.plot_spiderweb())                               # needs sage.plot

Polygon approximation of a circle:

sage: from cmath import exp
sage: pts = [exp(1j * t / 25) for t in range(25)]
sage: cs = complex_cubic_spline(pts)
sage: cs.derivative(2)
(-0.0497765406583...+0.151095006434...j)

>>> from sage.all import *
>>> from cmath import exp
>>> pts = [exp(ComplexNumber(0, '1') * t / Integer(25)) for t in range(Integer(25))]
>>> cs = complex_cubic_spline(pts)
>>> cs.derivative(Integer(2))
(-0.0497765406583...+0.151095006434...j)
sage.calculus.interpolators.polygon_spline(pts)[source]

Create a polygon from a set of complex or \((x,y)\) points. The polygon will be a parametric curve from 0 to 2*pi. The returned values will be complex, not \((x,y)\).

INPUT:

  • pts – list or array of complex numbers of tuples of the form \((x,y)\)

EXAMPLES:

A simple square:

sage: pts = [(-1, -1), (1, -1), (1, 1), (-1, 1)]
sage: ps = polygon_spline(pts)
sage: fx = lambda x: ps.value(x).real
sage: fy = lambda x: ps.value(x).imag
sage: show(parametric_plot((fx, fy), (0, 2*pi)))                                # needs sage.plot sage.symbolic
sage: m = Riemann_Map([lambda x: ps.value(real(x))],
....:                 [lambda x: ps.derivative(real(x))], 0)
sage: show(m.plot_colored() + m.plot_spiderweb())                               # needs sage.plot

>>> from sage.all import *
>>> pts = [(-Integer(1), -Integer(1)), (Integer(1), -Integer(1)), (Integer(1), Integer(1)), (-Integer(1), Integer(1))]
>>> ps = polygon_spline(pts)
>>> fx = lambda x: ps.value(x).real
>>> fy = lambda x: ps.value(x).imag
>>> show(parametric_plot((fx, fy), (Integer(0), Integer(2)*pi)))                                # needs sage.plot sage.symbolic
>>> m = Riemann_Map([lambda x: ps.value(real(x))],
...                 [lambda x: ps.derivative(real(x))], Integer(0))
>>> show(m.plot_colored() + m.plot_spiderweb())                               # needs sage.plot

Polygon approximation of a circle:

sage: # needs sage.symbolic
sage: pts = [e^(I*t / 25) for t in range(25)]
sage: ps = polygon_spline(pts)
sage: ps.derivative(2)
(-0.0470303661...+0.1520363883...j)

>>> from sage.all import *
>>> # needs sage.symbolic
>>> pts = [e**(I*t / Integer(25)) for t in range(Integer(25))]
>>> ps = polygon_spline(pts)
>>> ps.derivative(Integer(2))
(-0.0470303661...+0.1520363883...j)