2 :mod:`cmath` --- Mathematical functions for complex numbers
3 ===========================================================
6 :synopsis: Mathematical functions for complex numbers.
9 This module is always available. It provides access to mathematical functions
10 for complex numbers. The functions in this module accept integers,
11 floating-point numbers or complex numbers as arguments. They will also accept
12 any Python object that has either a :meth:`__complex__` or a :meth:`__float__`
13 method: these methods are used to convert the object to a complex or
14 floating-point number, respectively, and the function is then applied to the
15 result of the conversion.
19 On platforms with hardware and system-level support for signed
20 zeros, functions involving branch cuts are continuous on *both*
21 sides of the branch cut: the sign of the zero distinguishes one
22 side of the branch cut from the other. On platforms that do not
23 support signed zeros the continuity is as specified below.
29 Complex numbers can be expressed by two important coordinate systems.
30 Python's :class:`complex` type uses rectangular coordinates where a number
31 on the complex plain is defined by two floats, the real part and the imaginary
41 In engineering the polar coordinate system is popular for complex numbers. In
42 polar coordinates a complex number is defined by the radius *r* and the phase
43 angle *phi*. The radius *r* is the absolute value of the complex, which can be
44 viewed as distance from (0, 0). The radius *r* is always 0 or a positive float.
45 The phase angle *phi* is the counter clockwise angle from the positive x axis,
46 e.g. *1* has the angle *0*, *1j* has the angle *π/2* and *-1* the angle *-π*.
49 While :func:`phase` and func:`polar` return *+π* for a negative real they
50 may return *-π* for a complex with a very small negative imaginary
51 part, e.g. *-1-1E-300j*.
59 r := abs(z) := sqrt(real(z)**2 + imag(z)**2)
60 phi := phase(z) := atan2(imag(z), real(z))
61 cis(phi) := cos(phi) + 1j * sin(phi)
64 .. function:: phase(x)
66 Return phase, also known as the argument, of a complex.
71 .. function:: polar(x)
73 Convert a :class:`complex` from rectangular coordinates to polar
74 coordinates. The function returns a tuple with the two elements
75 *r* and *phi*. *r* is the distance from 0 and *phi* the phase
81 .. function:: rect(r, phi)
83 Convert from polar coordinates to rectangular coordinates and return
95 Return the arc cosine of *x*. There are two branch cuts: One extends right from
96 1 along the real axis to ∞, continuous from below. The other extends left from
97 -1 along the real axis to -∞, continuous from above.
100 .. function:: acosh(x)
102 Return the hyperbolic arc cosine of *x*. There is one branch cut, extending left
103 from 1 along the real axis to -∞, continuous from above.
106 .. function:: asin(x)
108 Return the arc sine of *x*. This has the same branch cuts as :func:`acos`.
111 .. function:: asinh(x)
113 Return the hyperbolic arc sine of *x*. There are two branch cuts:
114 One extends from ``1j`` along the imaginary axis to ``∞j``,
115 continuous from the right. The other extends from ``-1j`` along
116 the imaginary axis to ``-∞j``, continuous from the left.
118 .. versionchanged:: 2.6
119 branch cuts moved to match those recommended by the C99 standard
122 .. function:: atan(x)
124 Return the arc tangent of *x*. There are two branch cuts: One extends from
125 ``1j`` along the imaginary axis to ``∞j``, continuous from the right. The
126 other extends from ``-1j`` along the imaginary axis to ``-∞j``, continuous
129 .. versionchanged:: 2.6
130 direction of continuity of upper cut reversed
133 .. function:: atanh(x)
135 Return the hyperbolic arc tangent of *x*. There are two branch cuts: One
136 extends from ``1`` along the real axis to ``∞``, continuous from below. The
137 other extends from ``-1`` along the real axis to ``-∞``, continuous from
140 .. versionchanged:: 2.6
141 direction of continuity of right cut reversed
146 Return the cosine of *x*.
149 .. function:: cosh(x)
151 Return the hyperbolic cosine of *x*.
156 Return the exponential value ``e**x``.
159 .. function:: isinf(x)
161 Return *True* if the real or the imaginary part of x is positive
162 or negative infinity.
164 .. versionadded:: 2.6
167 .. function:: isnan(x)
169 Return *True* if the real or imaginary part of x is not a number (NaN).
171 .. versionadded:: 2.6
174 .. function:: log(x[, base])
176 Returns the logarithm of *x* to the given *base*. If the *base* is not
177 specified, returns the natural logarithm of *x*. There is one branch cut, from 0
178 along the negative real axis to -∞, continuous from above.
180 .. versionchanged:: 2.4
181 *base* argument added.
184 .. function:: log10(x)
186 Return the base-10 logarithm of *x*. This has the same branch cut as
192 Return the sine of *x*.
195 .. function:: sinh(x)
197 Return the hyperbolic sine of *x*.
200 .. function:: sqrt(x)
202 Return the square root of *x*. This has the same branch cut as :func:`log`.
207 Return the tangent of *x*.
210 .. function:: tanh(x)
212 Return the hyperbolic tangent of *x*.
214 The module also defines two mathematical constants:
219 The mathematical constant *pi*, as a float.
224 The mathematical constant *e*, as a float.
226 .. index:: module: math
228 Note that the selection of functions is similar, but not identical, to that in
229 module :mod:`math`. The reason for having two modules is that some users aren't
230 interested in complex numbers, and perhaps don't even know what they are. They
231 would rather have ``math.sqrt(-1)`` raise an exception than return a complex
232 number. Also note that the functions defined in :mod:`cmath` always return a
233 complex number, even if the answer can be expressed as a real number (in which
234 case the complex number has an imaginary part of zero).
236 A note on branch cuts: They are curves along which the given function fails to
237 be continuous. They are a necessary feature of many complex functions. It is
238 assumed that if you need to compute with complex functions, you will understand
239 about branch cuts. Consult almost any (not too elementary) book on complex
240 variables for enlightenment. For information of the proper choice of branch
241 cuts for numerical purposes, a good reference should be the following:
246 Kahan, W: Branch cuts for complex elementary functions; or, Much ado about
247 nothing's sign bit. In Iserles, A., and Powell, M. (eds.), The state of the art
248 in numerical analysis. Clarendon Press (1987) pp165-211.