Python語言的數學函數

 

5.7 math -- Mathematical functions

This module is always available. It provides access to the mathematical functions defined by the C standard.

These functions cannot be used with complex numbers; use the functions of the same name from the cmath module if you require support for complex numbers. The distinction between functions which support complex numbers and those which don't is made since most users do not want to learn quite as much mathematics as required to understand complex numbers. Receiving an exception instead of a complex result allows earlier detection of the unexpected complex number used as a parameter, so that the programmer can determine how and why it was generated in the first place.

The following functions are provided by this module. Except when explicitly noted otherwise, all return values are floats.

Number-theoretic and representation functions:

 

ceil(

x)

Return the ceiling of x as a float, the smallest integer value greater than or equal to x.

 

fabs(

x)

Return the absolute value of x.

 

floor(

x)

Return the floor of x as a float, the largest integer value less than or equal to x.

 

fmod(

x, y)

Return fmod(x, y), as defined by the platform C library. Note that the Python expression x % y may not return the same result. The intent of the C standard is that fmod(x, y) be exactly (mathematically; to infinite precision) equal to x - n*y for some integer n such that the result has the same sign as x and magnitude less than abs(y). Python's x % y returns a result with the sign of y instead, and may not be exactly computable for float arguments. For example, fmod(-1e-100, 1e100) is -1e-100, but the result of Python's -1e-100 % 1e100 is 1e100-1e-100, which cannot be represented exactly as a float, and rounds to the surprising 1e100. For this reason, function fmod() is generally preferred when working with floats, while Python's x % y is preferred when working with integers.

 

frexp(

x)

Return the mantissa and exponent of x as the pair (m, e). m is a float and e is an integer such that x == m * 2**e exactly. If x is zero, returns (0.0, 0), otherwise 0.5 <= abs(m) < 1. This is used to "pick apart" the internal representation of a float in a portable way.

 

ldexp(

x, i)

Return x * (2**i). This is essentially the inverse of function frexp().

 

modf(

x)

Return the fractional and integer parts of x. Both results carry the sign of x, and both are floats.

Note that frexp() and modf() have a different call/return pattern than their C equivalents: they take a single argument and return a pair of values, rather than returning their second return value through an `output parameter' (there is no such thing in Python).

For the ceil(), floor(), and modf() functions, note that all floating-point numbers of sufficiently large magnitude are exact integers. Python floats typically carry no more than 53 bits of precision (the same as the platform C double type), in which case any float x with abs(x) >= 2**52 necessarily has no fractional bits.

Power and logarithmic functions:

 

exp(

x)

Return e**x.

 

log(	x[, base])

Return the logarithm of x to the given base. If the base is not specified, return the natural logarithm of x (that is, the logarithm to base e). Changed in version 2.3: base argument added.

 

log10(

x)

Return the base-10 logarithm of x.

 

pow(

x, y)

Return x**y.

 

sqrt(

x)

Return the square root of x.

Trigonometric functions:

 

acos(

x)

Return the arc cosine of x, in radians.

 

asin(

x)

Return the arc sine of x, in radians.

 

atan(

x)

Return the arc tangent of x, in radians.

 

atan2(

y, x)

Return atan(y / x), in radians. The result is between -pi and pi. The vector in the plane from the origin to point (x, y) makes this angle with the positive X axis. The point of atan2() is that the signs of both inputs are known to it, so it can compute the correct quadrant for the angle. For example, atan(1) and atan2(1, 1) are both pi/4, but atan2(-1, -1) is -3*pi/4.

 

cos(

x)

Return the cosine of x radians.

 

hypot(

x, y)

Return the Euclidean norm, sqrt(x*x + y*y). This is the length of the vector from the origin to point (x, y).

 

sin(

x)

Return the sine of x radians.

 

tan(

x)

Return the tangent of x radians.

Angular conversion:

 

degrees(

x)

Converts angle x from radians to degrees.

 

radians(

x)

Converts angle x from degrees to radians.

Hyperbolic functions:

 

cosh(

x)

Return the hyperbolic cosine of x.

 

sinh(

x)

Return the hyperbolic sine of x.

 

tanh(

x)

Return the hyperbolic tangent of x.

The module also defines two mathematical constants:

 

pi

The mathematical constant pi.

 

e

The mathematical constant e.

 

Note: The math module consists mostly of thin wrappers around the platform C math library functions. Behavior in exceptional cases is loosely specified by the C standards, and Python inherits much of its math-function error-reporting behavior from the platform C implementation. As a result, the specific exceptions raised in error cases (and even whether some arguments are considered to be exceptional at all) are not defined in any useful cross-platform or cross-release way. For example, whether math.log(0) returns -Inf or raises ValueError or OverflowError isn't defined, and in cases where math.log(0) raises OverflowError, math.log(0L) may raise ValueError instead.

 

See Also:

Module cmath:

Complex number versions of many of these functions.