On this page本页内容
$tanh New in version 4.2.在版本4.2中新增。
Returns the hyperbolic tangent of a value that is measured in radians.返回以弧度度量的值的双曲正切。
$tanh has the following syntax:语法如下：
{ $tanh: <expression> }
$tanh takes any valid expression that resolves to a number, measured in radians. 接受解析为数字（以弧度为单位）的任何有效表达式。If the expression returns a value in degrees, use the 如果表达式返回以度为单位的值，请使用$degreesToRadians operator to convert the value to radians.$degreesToRadians运算符将该值转换为弧度。
By default 默认情况下，$tanh returns values as a double. $tanh以double形式返回值。$tanh can also return values as a 128-bit decimal if the <expression> resolves to a 128-bit decimal value.<expression>解析为128位十进制值，$tanh还可以将值返回为128位十进制数。
For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。
null, NaN, and +/- InfinityIf the input argument resolves to a value of 如果输入参数解析为null or refers to a field that is missing, $tanh returns null. null值或引用缺少的字段，$tanh将返回null。If the argument resolves to 如果参数解析为NaN, $tanh returns NaN. NaN，$tanh将返回NaN。If the argument resolves to negative or positive 如果参数解析为负Infinity, $tanh returns -1 or 1 respectively.Infinity或正Infinity，$tanh将分别返回-1或1。
{ $tanh: NaN } | NaN |
{ $tanh: null } | null |
{ $tanh: -Infinity } | -1 |
{ $tanh: Infinity } | 1 |
The following 以下trigonometry collection contains a document that stores an angle value measured in degrees:trigonometry集合包含一个文档，该文档存储以度为单位的angle值：
db.trigonometry.insertOne( { "_id" : ObjectId( "5c50782193f833234ba90d45" ), "angle" : NumberDecimal( "53.1301023541559787031443874490659" ) } )
The following aggregation operation uses the 以下聚合操作使用$tanh expression to calculate the hyperbolic tangent of angle and adds it to the input document using the $addFields pipeline stage:$tanh表达式计算angle的双曲正切，并使用$addFields管道阶段将其添加到输入文档中：
db.trigonometry.aggregate( [ { $addFields : { "tanh_output" : { $tanh : { $degreesToRadians : "$angle" } } } } ] )
The $degreesToRadians expression converts the angle in degrees to radians.$degreesToRadians表达式将角度（以度为单位）转换为弧度。
Example output:输出示例：
{
"_id" : ObjectId("5c50782193f833234ba90d45"),
"angle" : NumberDecimal("53.1301023541559787031443874490659"),
"tanh_output" : NumberDecimal("0.7293303448445332820512777329448416")
}Because 因为angle is stored as a 128-bit decimal, the $tanh output is also a 128-bit decimal.angle存储为128位十进制，所以$tanh输出也是128位十进制。
The following 以下trigonometry collection contains a document that stores an angle value measured in radians:trigonometry集合包含一个文档，该文档存储以弧度度量的角度值：
db.trigonometry.insertOne( { "_id" : ObjectId( "5c50782193f833234ba90d55" ), "angle" : NumberDecimal( "1.6301023541559787031443874490659" ) } )
The following aggregation operation uses the 以下聚合操作使用$tanh expression to calculate the hyperbolic tangent of angle and adds it to the input document using the $addFields pipeline stage:$tanh表达式计算angle的双曲正切，并使用$addFields管道阶段将其添加到输入文档中：
db.trigonometry.aggregate( [ { $addFields : { "tanh_output" : { $tanh : "$angle" } } } ] )
Example output:输出示例：
{
"_id" : ObjectId("5c50782193f833234ba90d55"),
"angle" : NumberDecimal("1.6301023541559787031443874490659"),
"tanh_output" : NumberDecimal("0.9260761562750713360156803177935379")
}Because 因为angle is stored as a 128-bit decimal, the $tanh output is also a 128-bit decimal.angle存储为128位十进制，所以$tanh输出也是128位十进制。