# package math
`import "math"`
math包提供了基本的数学常数和数学函数。
## Index
* [Constants](#pkg-constants)
* [func NaN() float64](#NaN)
* [func IsNaN(f float64) (is bool)](#IsNaN)
* [func Inf(sign int) float64](#Inf)
* [func IsInf(f float64, sign int) bool](#IsInf)
* [func Float32bits(f float32) uint32](#Float32bits)
* [func Float32frombits(b uint32) float32](#Float32frombits)
* [func Float64bits(f float64) uint64](#Float64bits)
* [func Float64frombits(b uint64) float64](#Float64frombits)
* [func Signbit(x float64) bool](#Signbit)
* [func Copysign(x, y float64) float64](#Copysign)
* [func Ceil(x float64) float64](#Ceil)
* [func Floor(x float64) float64](#Floor)
* [func Trunc(x float64) float64](#Trunc)
* [func Modf(f float64) (int float64, frac float64)](#Modf)
* [func Nextafter(x, y float64) (r float64)](#Nextafter)
* [func Abs(x float64) float64](#Abs)
* [func Max(x, y float64) float64](#Max)
* [func Min(x, y float64) float64](#Min)
* [func Dim(x, y float64) float64](#Dim)
* [func Mod(x, y float64) float64](#Mod)
* [func Remainder(x, y float64) float64](#Remainder)
* [func Sqrt(x float64) float64](#Sqrt)
* [func Cbrt(x float64) float64](#Cbrt)
* [func Hypot(p, q float64) float64](#Hypot)
* [func Sin(x float64) float64](#Sin)
* [func Cos(x float64) float64](#Cos)
* [func Tan(x float64) float64](#Tan)
* [func Sincos(x float64) (sin, cos float64)](#Sincos)
* [func Asin(x float64) float64](#Asin)
* [func Acos(x float64) float64](#Acos)
* [func Atan(x float64) float64](#Atan)
* [func Atan2(y, x float64) float64](#Atan2)
* [func Sinh(x float64) float64](#Sinh)
* [func Cosh(x float64) float64](#Cosh)
* [func Tanh(x float64) float64](#Tanh)
* [func Asinh(x float64) float64](#Asinh)
* [func Acosh(x float64) float64](#Acosh)
* [func Atanh(x float64) float64](#Atanh)
* [func Log(x float64) float64](#Log)
* [func Log1p(x float64) float64](#Log1p)
* [func Log2(x float64) float64](#Log2)
* [func Log10(x float64) float64](#Log10)
* [func Logb(x float64) float64](#Logb)
* [func Ilogb(x float64) int](#Ilogb)
* [func Frexp(f float64) (frac float64, exp int)](#Frexp)
* [func Ldexp(frac float64, exp int) float64](#Ldexp)
* [func Exp(x float64) float64](#Exp)
* [func Expm1(x float64) float64](#Expm1)
* [func Exp2(x float64) float64](#Exp2)
* [func Pow(x, y float64) float64](#Pow)
* [func Pow10(e int) float64](#Pow10)
* [func Gamma(x float64) float64](#Gamma)
* [func Lgamma(x float64) (lgamma float64, sign int)](#Lgamma)
* [func Erf(x float64) float64](#Erf)
* [func Erfc(x float64) float64](#Erfc)
* [func J0(x float64) float64](#J0)
* [func J1(x float64) float64](#J1)
* [func Jn(n int, x float64) float64](#Jn)
* [func Y0(x float64) float64](#Y0)
* [func Y1(x float64) float64](#Y1)
* [func Yn(n int, x float64) float64](#Yn)
## Constants
```
const (
E = 2.71828182845904523536028747135266249775724709369995957496696763 // A001113
Pi = 3.14159265358979323846264338327950288419716939937510582097494459 // A000796
Phi = 1.61803398874989484820458683436563811772030917980576286213544862 // A001622
Sqrt2 = 1.41421356237309504880168872420969807856967187537694807317667974 // A002193
SqrtE = 1.64872127070012814684865078781416357165377610071014801157507931 // A019774
SqrtPi = 1.77245385090551602729816748334114518279754945612238712821380779 // A002161
SqrtPhi = 1.27201964951406896425242246173749149171560804184009624861664038 // A139339
Ln2 = 0.693147180559945309417232121458176568075500134360255254120680009 // A002162
Log2E = 1 / Ln2
Ln10 = 2.30258509299404568401799145468436420760110148862877297603332790 // A002392
Log10E = 1 / Ln10
)
```
数学常数，参见：[http://oeis.org/Axxxxxx](http://oeis.org/Axxxxxx)
```
const (
MaxFloat32 = 3.40282346638528859811704183484516925440e+38 // 2**127 * (2**24 - 1) / 2**23
SmallestNonzeroFloat32 = 1.401298464324817070923729583289916131280e-45 // 1 / 2**(127 - 1 + 23)
MaxFloat64 = 1.797693134862315708145274237317043567981e+308 // 2**1023 * (2**53 - 1) / 2**52
SmallestNonzeroFloat64 = 4.940656458412465441765687928682213723651e-324 // 1 / 2**(1023 - 1 + 52)
)
```
浮点数的取值极限。Max是该类型所能表示的最大有限值；SmallestNonzero是该类型所能表示的最小非零正数值。
```
const (
MaxInt8 = 1<<7 - 1
MinInt8 = -1 << 7
MaxInt16 = 1<<15 - 1
MinInt16 = -1 << 15
MaxInt32 = 1<<31 - 1
MinInt32 = -1 << 31
MaxInt64 = 1<<63 - 1
MinInt64 = -1 << 63
MaxUint8 = 1<<8 - 1
MaxUint16 = 1<<16 - 1
MaxUint32 = 1<<32 - 1
MaxUint64 = 1<<64 - 1
)
```
整数的取值极限。
## func [NaN](https://github.com/golang/go/blob/master/src/math/bits.go#L28 "View Source")
```
func NaN() float64
```
函数返回一个IEEE 754“这不是一个数字”值。
## func [IsNaN](https://github.com/golang/go/blob/master/src/math/bits.go#L31 "View Source")
```
func IsNaN(f float64) (is bool)
```
报告f是否表示一个NaN（Not A Number）值。
## func [Inf](https://github.com/golang/go/blob/master/src/math/bits.go#L17 "View Source")
```
func Inf(sign int) float64
```
如果sign>=0函数返回正无穷大，否则返回负无穷大。
## func [IsInf](https://github.com/golang/go/blob/master/src/math/bits.go#L43 "View Source")
```
func IsInf(f float64, sign int) bool
```
如果sign > 0，f是正无穷大时返回真；如果sign<0，f是负无穷大时返回真；sign==0则f是两种无穷大时都返回真。
## func [Float32bits](https://github.com/golang/go/blob/master/src/math/unsafe.go#L10 "View Source")
```
func Float32bits(f float32) uint32
```
函数返回浮点数f的IEEE 754格式二进制表示对应的4字节无符号整数。
## func [Float32frombits](https://github.com/golang/go/blob/master/src/math/unsafe.go#L14 "View Source")
```
func Float32frombits(b uint32) float32
```
函数返回无符号整数b对应的IEEE 754格式二进制表示的4字节浮点数。
## func [Float64bits](https://github.com/golang/go/blob/master/src/math/unsafe.go#L17 "View Source")
```
func Float64bits(f float64) uint64
```
函数返回浮点数f的IEEE 754格式二进制表示对应的8字节无符号整数。
## func [Float64frombits](https://github.com/golang/go/blob/master/src/math/unsafe.go#L21 "View Source")
```
func Float64frombits(b uint64) float64
```
函数返回无符号整数b对应的IEEE 754格式二进制表示的8字节浮点数。
## func [Signbit](https://github.com/golang/go/blob/master/src/math/signbit.go#L8 "View Source")
```
func Signbit(x float64) bool
```
如果x是一个负数或者负零，返回真。
## func [Copysign](https://github.com/golang/go/blob/master/src/math/copysign.go#L9 "View Source")
```
func Copysign(x, y float64) float64
```
返回拥有x的量值（绝对值）和y的标志位（正负号）的浮点数。
## func [Ceil](https://github.com/golang/go/blob/master/src/math/floor.go#L36 "View Source")
```
func Ceil(x float64) float64
```
返回不小于x的最小整数（的浮点值），特例如下：
```
Ceil(±0) = ±0
Ceil(±Inf) = ±Inf
Ceil(NaN) = NaN
```
## func [Floor](https://github.com/golang/go/blob/master/src/math/floor.go#L13 "View Source")
```
func Floor(x float64) float64
```
返回不大于x的最小整数（的浮点值），特例如下：
```
Floor(±0) = ±0
Floor(±Inf) = ±Inf
Floor(NaN) = NaN
```
## func [Trunc](https://github.com/golang/go/blob/master/src/math/floor.go#L48 "View Source")
```
func Trunc(x float64) float64
```
返回x的整数部分（的浮点值）。特例如下：
```
Trunc(±0) = ±0
Trunc(±Inf) = ±Inf
Trunc(NaN) = NaN
```
## func [Modf](https://github.com/golang/go/blob/master/src/math/modf.go#L13 "View Source")
```
func Modf(f float64) (int float64, frac float64)
```
返回f的整数部分和小数部分，结果的正负号和都x相同；特例如下：
```
Modf(±Inf) = ±Inf, NaN
Modf(NaN) = NaN, NaN
```
## func [Nextafter](https://github.com/golang/go/blob/master/src/math/nextafter.go#L13 "View Source")
```
func Nextafter(x, y float64) (r float64)
```
参数x到参数y的方向上，下一个可表示的数值；如果x==y将返回x。特例如下：
```
Nextafter(NaN, y) = NaN
Nextafter(x, NaN) = NaN
```
## func [Abs](https://github.com/golang/go/blob/master/src/math/abs.go#L12 "View Source")
```
func Abs(x float64) float64
```
返回x的绝对值；特例如下：
```
Abs(±Inf) = +Inf
Abs(NaN) = NaN
```
## func [Max](https://github.com/golang/go/blob/master/src/math/dim.go#L26 "View Source")
```
func Max(x, y float64) float64
```
返回x和y中最大值，特例如下：
```
Max(x, +Inf) = Max(+Inf, x) = +Inf
Max(x, NaN) = Max(NaN, x) = NaN
Max(+0, ±0) = Max(±0, +0) = +0
Max(-0, -0) = -0
```
## func [Min](https://github.com/golang/go/blob/master/src/math/dim.go#L53 "View Source")
```
func Min(x, y float64) float64
```
返回x和y中最小值，特例如下：
```
Min(x, -Inf) = Min(-Inf, x) = -Inf
Min(x, NaN) = Min(NaN, x) = NaN
Min(-0, ±0) = Min(±0, -0) = -0
```
## func [Dim](https://github.com/golang/go/blob/master/src/math/dim.go#L13 "View Source")
```
func Dim(x, y float64) float64
```
函数返回x-y和0中的最大值，特殊情况：
```
Dim(+Inf, +Inf) = NaN
Dim(-Inf, -Inf) = NaN
Dim(x, NaN) = Dim(NaN, x) = NaN
```
## func [Mod](https://github.com/golang/go/blob/master/src/math/mod.go#L21 "View Source")
```
func Mod(x, y float64) float64
```
取余运算，可以理解为 x-Trunc(x/y)\*y，结果的正负号和x相同；特例如下：
```
Mod(±Inf, y) = NaN
Mod(NaN, y) = NaN
Mod(x, 0) = NaN
Mod(x, ±Inf) = x
Mod(x, NaN) = NaN
```
## func [Remainder](https://github.com/golang/go/blob/master/src/math/remainder.go#L37 "View Source")
```
func Remainder(x, y float64) float64
```
IEEE 754差数求值，即x减去最接近x/y的整数值（如果有两个整数与x/y距离相同，则取其中的偶数）与y的乘积。特例如下：
```
Remainder(±Inf, y) = NaN
Remainder(NaN, y) = NaN
Remainder(x, 0) = NaN
Remainder(x, ±Inf) = x
Remainder(x, NaN) = NaN
```
## func [Sqrt](https://github.com/golang/go/blob/master/src/math/sqrt.go#L92 "View Source")
```
func Sqrt(x float64) float64
```
返回x的二次方根，特例如下：
```
Sqrt(+Inf) = +Inf
Sqrt(±0) = ±0
Sqrt(x < 0) = NaN
Sqrt(NaN) = NaN
```
## func [Cbrt](https://github.com/golang/go/blob/master/src/math/cbrt.go#L21 "View Source")
```
func Cbrt(x float64) float64
```
返回x的三次方根，特例如下：
```
Cbrt(±0) = ±0
Cbrt(±Inf) = ±Inf
Cbrt(NaN) = NaN
```
## func [Hypot](https://github.com/golang/go/blob/master/src/math/hypot.go#L19 "View Source")
```
func Hypot(p, q float64) float64
```
返回Sqrt(p\*p + q\*q)，注意要避免不必要的溢出或下溢。特例如下：
```
Hypot(±Inf, q) = +Inf
Hypot(p, ±Inf) = +Inf
Hypot(NaN, q) = NaN
Hypot(p, NaN) = NaN
```
## func [Sin](https://github.com/golang/go/blob/master/src/math/sin.go#L174 "View Source")
```
func Sin(x float64) float64
```
求正弦。特例如下：
```
Sin(±0) = ±0
Sin(±Inf) = NaN
Sin(NaN) = NaN
```
## func [Cos](https://github.com/golang/go/blob/master/src/math/sin.go#L117 "View Source")
```
func Cos(x float64) float64
```
求余弦。特例如下：
```
Cos(±Inf) = NaN
Cos(NaN) = NaN
```
## func [Tan](https://github.com/golang/go/blob/master/src/math/tan.go#L82 "View Source")
```
func Tan(x float64) float64
```
求正切。特例如下：
```
Tan(±0) = ±0
Tan(±Inf) = NaN
Tan(NaN) = NaN
```
## func [Sincos](https://github.com/golang/go/blob/master/src/math/sincos.go#L15 "View Source")
```
func Sincos(x float64) (sin, cos float64)
```
函数返回Sin(x), Cos(x)。特例如下：
```
Sincos(±0) = ±0, 1
Sincos(±Inf) = NaN, NaN
Sincos(NaN) = NaN, NaN
```
## func [Asin](https://github.com/golang/go/blob/master/src/math/asin.go#L19 "View Source")
```
func Asin(x float64) float64
```
求反正弦（x是弧度）。特例如下：
```
Asin(±0) = ±0
Asin(x) = NaN if x < -1 or x > 1
```
## func [Acos](https://github.com/golang/go/blob/master/src/math/asin.go#L51 "View Source")
```
func Acos(x float64) float64
```
求反余弦（x是弧度）。特例如下：
```
Acos(x) = NaN if x < -1 or x > 1
```
## func [Atan](https://github.com/golang/go/blob/master/src/math/atan.go#L95 "View Source")
```
func Atan(x float64) float64
```
求反正切（x是弧度）。特例如下：
```
Atan(±0) = ±0
Atan(±Inf) = ±Pi/2
```
## func [Atan2](https://github.com/golang/go/blob/master/src/math/atan2.go#L29 "View Source")
```
func Atan2(y, x float64) float64
```
类似Atan(y/x)，但会根据x，y的正负号确定象限。特例如下（前面的优先）：
```
Atan2(y, NaN) = NaN
Atan2(NaN, x) = NaN
Atan2(+0, x>=0) = +0
Atan2(-0, x>=0) = -0
Atan2(+0, x<=-0) = +Pi
Atan2(-0, x<=-0) = -Pi
Atan2(y>0, 0) = +Pi/2
Atan2(y<0, 0) = -Pi/2
Atan2(+Inf, +Inf) = +Pi/4
Atan2(-Inf, +Inf) = -Pi/4
Atan2(+Inf, -Inf) = 3Pi/4
Atan2(-Inf, -Inf) = -3Pi/4
Atan2(y, +Inf) = 0
Atan2(y>0, -Inf) = +Pi
Atan2(y<0, -Inf) = -Pi
Atan2(+Inf, x) = +Pi/2
Atan2(-Inf, x) = -Pi/2
```
## func [Sinh](https://github.com/golang/go/blob/master/src/math/sinh.go#L25 "View Source")
```
func Sinh(x float64) float64
```
求双曲正弦，特例如下：
```
Sinh(±0) = ±0
Sinh(±Inf) = ±Inf
Sinh(NaN) = NaN
```
## func [Cosh](https://github.com/golang/go/blob/master/src/math/sinh.go#L69 "View Source")
```
func Cosh(x float64) float64
```
求双曲余弦，特例如下：
```
Cosh(±0) = 1
Cosh(±Inf) = +Inf
Cosh(NaN) = NaN
```
## func [Tanh](https://github.com/golang/go/blob/master/src/math/tanh.go#L74 "View Source")
```
func Tanh(x float64) float64
```
求双曲正切，特例如下：
```
Tanh(±0) = ±0
Tanh(±Inf) = ±1
Tanh(NaN) = NaN
```
## func [Asinh](https://github.com/golang/go/blob/master/src/math/asinh.go#L39 "View Source")
```
func Asinh(x float64) float64
```
求反双曲正弦，特例如下：
```
Asinh(±0) = ±0
Asinh(±Inf) = ±Inf
Asinh(NaN) = NaN
```
## func [Acosh](https://github.com/golang/go/blob/master/src/math/acosh.go#L42 "View Source")
```
func Acosh(x float64) float64
```
求反双曲余弦，特例如下：
```
Acosh(+Inf) = +Inf
Acosh(x) = NaN if x < 1
Acosh(NaN) = NaN
```
## func [Atanh](https://github.com/golang/go/blob/master/src/math/atanh.go#L47 "View Source")
```
func Atanh(x float64) float64
```
求反双曲正切，特例如下：
```
Atanh(1) = +Inf
Atanh(±0) = ±0
Atanh(-1) = -Inf
Atanh(x) = NaN if x < -1 or x > 1
Atanh(NaN) = NaN
```
## func [Log](https://github.com/golang/go/blob/master/src/math/log.go#L80 "View Source")
```
func Log(x float64) float64
```
求自然对数，特例如下：
```
Log(+Inf) = +Inf
Log(0) = -Inf
Log(x < 0) = NaN
Log(NaN) = NaN
```
## func [Log1p](https://github.com/golang/go/blob/master/src/math/log1p.go#L95 "View Source")
```
func Log1p(x float64) float64
```
等价于Log(1+x)。但是在x接近0时，本函数更加精确；特例如下：
```
Log1p(+Inf) = +Inf
Log1p(±0) = ±0
Log1p(-1) = -Inf
Log1p(x < -1) = NaN
Log1p(NaN) = NaN
```
## func [Log2](https://github.com/golang/go/blob/master/src/math/log10.go#L17 "View Source")
```
func Log2(x float64) float64
```
求2为底的对数；特例和Log相同。
## func [Log10](https://github.com/golang/go/blob/master/src/math/log10.go#L9 "View Source")
```
func Log10(x float64) float64
```
求10为底的对数；特例和Log相同。
## func [Logb](https://github.com/golang/go/blob/master/src/math/logb.go#L13 "View Source")
```
func Logb(x float64) float64
```
返回x的二进制指数值，可以理解为Trunc(Log2(x))；特例如下：
```
Logb(±Inf) = +Inf
Logb(0) = -Inf
Logb(NaN) = NaN
```
## func [Ilogb](https://github.com/golang/go/blob/master/src/math/logb.go#L32 "View Source")
```
func Ilogb(x float64) int
```
类似Logb，但返回值是整型；特例如下：
```
Ilogb(±Inf) = MaxInt32
Ilogb(0) = MinInt32
Ilogb(NaN) = MaxInt32
```
## func [Frexp](https://github.com/golang/go/blob/master/src/math/frexp.go#L16 "View Source")
```
func Frexp(f float64) (frac float64, exp int)
```
返回一个标准化小数frac和2的整型指数exp，满足f == frac \* 2\*\*exp，且0.5 <= Abs(frac) < 1；特例如下：
```
Frexp(±0) = ±0, 0
Frexp(±Inf) = ±Inf, 0
Frexp(NaN) = NaN, 0
```
## func [Ldexp](https://github.com/golang/go/blob/master/src/math/ldexp.go#L14 "View Source")
```
func Ldexp(frac float64, exp int) float64
```
Frexp的反函数，返回 frac \* 2\*\*exp。特例如下：
```
Ldexp(±0, exp) = ±0
Ldexp(±Inf, exp) = ±Inf
Ldexp(NaN, exp) = NaN
```
## func [Exp](https://github.com/golang/go/blob/master/src/math/exp.go#L14 "View Source")
```
func Exp(x float64) float64
```
返回E\*\*x；x绝对值很大时可能会溢出为0或者+Inf，x绝对值很小时可能会下溢为1。特例如下：
```
Exp(+Inf) = +Inf
Exp(NaN) = NaN
```
## func [Expm1](https://github.com/golang/go/blob/master/src/math/expm1.go#L124 "View Source")
```
func Expm1(x float64) float64
```
等价于Exp(x)-1，但是在x接近零时更精确；x绝对值很大时可能会溢出为-1或+Inf。特例如下：
```
Expm1(+Inf) = +Inf
Expm1(-Inf) = -1
Expm1(NaN) = NaN
```
## func [Exp2](https://github.com/golang/go/blob/master/src/math/exp.go#L135 "View Source")
```
func Exp2(x float64) float64
```
返回2\*\*x；特例和Exp相同。
## func [Pow](https://github.com/golang/go/blob/master/src/math/pow.go#L38 "View Source")
```
func Pow(x, y float64) float64
```
返回x\*\*y；特例如下（前面的优先）：
```
Pow(x, ±0) = 1 for any x
Pow(1, y) = 1 for any y
Pow(x, 1) = x for any x
Pow(NaN, y) = NaN
Pow(x, NaN) = NaN
Pow(±0, y) = ±Inf for y an odd integer < 0
Pow(±0, -Inf) = +Inf
Pow(±0, +Inf) = +0
Pow(±0, y) = +Inf for finite y < 0 and not an odd integer
Pow(±0, y) = ±0 for y an odd integer > 0
Pow(±0, y) = +0 for finite y > 0 and not an odd integer
Pow(-1, ±Inf) = 1
Pow(x, +Inf) = +Inf for |x| > 1
Pow(x, -Inf) = +0 for |x| > 1
Pow(x, +Inf) = +0 for |x| < 1
Pow(x, -Inf) = +Inf for |x| < 1
Pow(+Inf, y) = +Inf for y > 0
Pow(+Inf, y) = +0 for y < 0
Pow(-Inf, y) = Pow(-0, -y)
Pow(x, y) = NaN for finite x < 0 and finite non-integer y
```
## func [Pow10](https://github.com/golang/go/blob/master/src/math/pow10.go#L16 "View Source")
```
func Pow10(e int) float64
```
返回10\*\*e；特例如下：
```
Pow10(e) = +Inf for e > 309
Pow10(e) = 0 for e < -324
```
## func [Gamma](https://github.com/golang/go/blob/master/src/math/gamma.go#L122 "View Source")
```
func Gamma(x float64) float64
```
伽玛函数（当x为正整数时，值为(x-1)!）。特例如下：
```
Gamma(+Inf) = +Inf
Gamma(+0) = +Inf
Gamma(-0) = -Inf
Gamma(x) = NaN for integer x < 0
Gamma(-Inf) = NaN
Gamma(NaN) = NaN
```
## func [Lgamma](https://github.com/golang/go/blob/master/src/math/lgamma.go#L174 "View Source")
```
func Lgamma(x float64) (lgamma float64, sign int)
```
返回Gamma(x)的自然对数和正负号。特例如下：
```
Lgamma(+Inf) = +Inf
Lgamma(0) = +Inf
Lgamma(-integer) = +Inf
Lgamma(-Inf) = -Inf
Lgamma(NaN) = NaN
```
## func [Erf](https://github.com/golang/go/blob/master/src/math/erf.go#L188 "View Source")
```
func Erf(x float64) float64
```
误差函数，特例如下：
```
Erf(+Inf) = 1
Erf(-Inf) = -1
Erf(NaN) = NaN
```
## func [Erfc](https://github.com/golang/go/blob/master/src/math/erf.go#L265 "View Source")
```
func Erfc(x float64) float64
```
余补误差函数，特例如下：
```
Erfc(+Inf) = 0
Erfc(-Inf) = 2
Erfc(NaN) = NaN
```
## func [J0](https://github.com/golang/go/blob/master/src/math/j0.go#L76 "View Source")
```
func J0(x float64) float64
```
第一类贝塞尔函数，0阶。特例如下：
```
J0(±Inf) = 0
J0(0) = 1
J0(NaN) = NaN
```
## func [J1](https://github.com/golang/go/blob/master/src/math/j1.go#L74 "View Source")
```
func J1(x float64) float64
```
第一类贝塞尔函数，1阶。特例如下：
```
J1(±Inf) = 0
J1(NaN) = NaN
```
## func [Jn](https://github.com/golang/go/blob/master/src/math/jn.go#L53 "View Source")
```
func Jn(n int, x float64) float64
```
第一类贝塞尔函数，n阶。特例如下：
```
Jn(n, ±Inf) = 0
Jn(n, NaN) = NaN
```
## func [Y0](https://github.com/golang/go/blob/master/src/math/j0.go#L156 "View Source")
```
func Y0(x float64) float64
```
第二类贝塞尔函数，0阶。特例如下：
```
Y0(+Inf) = 0
Y0(0) = -Inf
Y0(x < 0) = NaN
Y0(NaN) = NaN
```
## func [Y1](https://github.com/golang/go/blob/master/src/math/j1.go#L154 "View Source")
```
func Y1(x float64) float64
```
第二类贝塞尔函数，1阶。特例如下：
```
Y1(+Inf) = 0
Y1(0) = -Inf
Y1(x < 0) = NaN
Y1(NaN) = NaN
```
## func [Yn](https://github.com/golang/go/blob/master/src/math/jn.go#L235 "View Source")
```
func Yn(n int, x float64) float64
```
第二类贝塞尔函数，n阶。特例如下：
```
Yn(n, +Inf) = 0
Yn(n > 0, 0) = -Inf
Yn(n < 0, 0) = +Inf if n is odd, -Inf if n is even
Y1(n, x < 0) = NaN
Y1(n, NaN) = NaN
```
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