$tanh以弧度为单位返回数值的双曲正切值。
$tanh通过以下语法实现：{ $tanh: <expression> } $tanhtakes any valid expression that resolves to a number, measured in radians. If the expression returns a value in degrees, use the$degreesToRadiansoperator to convert the value to radians.By default
$tanhreturns values as adouble.$tanhcan also return values as a 128-bit decimal if the<expression>resolves to a 128-bit decimal value.有关表达式的更多信息，请参阅表达式。
行为
null、NaN 和+/- Infinity
If the input argument resolves to a value of null or refers to a field that is missing, $tanh returns null. If the argument resolves to NaN, $tanh returns NaN. If the argument resolves to negative or positive Infinity, $tanh returns -1 or 1 respectively.
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例子
trigonometry以下collection包含一个文档，其中存储了一个以度数为单位的angle 值：
db.trigonometry.insertOne( { "_id" : ObjectId( "5c50782193f833234ba90d45" ), "angle" : Decimal128( "53.1301023541559787031443874490659" ) } )
The following aggregation operation uses the $tanh expression to calculate the hyperbolic tangent of angle and adds it to the input document using the $addFields pipeline stage:
db.trigonometry.aggregate( [ { $addFields : { "tanh_output" : { $tanh : { $degreesToRadians : "$angle" } } } } ] )
$degreesToRadians表达式将以度为单位的angle转换为弧度。
示例输出：
{ "_id" : ObjectId("5c50782193f833234ba90d45"), "angle" : Decimal128("53.1301023541559787031443874490659"), "tanh_output" : Decimal128("0.7293303448445332820512777329448416") }
Because angle is stored as a 128-bit decimal, the $tanh output is also a 128-bit decimal.
以下trigonometry集合包含一个文档，其中存储了以弧度为单位的angle值：
db.trigonometry.insertOne( { "_id" : ObjectId( "5c50782193f833234ba90d55" ), "angle" : Decimal128( "1.6301023541559787031443874490659" ) } )
The following aggregation operation uses the $tanh expression to calculate the hyperbolic tangent of angle and adds it to the input document using the $addFields pipeline stage:
db.trigonometry.aggregate( [ { $addFields : { "tanh_output" : { $tanh : "$angle" } } } ] )
示例输出：
{ "_id" : ObjectId("5c50782193f833234ba90d55"), "angle" : Decimal128("1.6301023541559787031443874490659"), "tanh_output" : Decimal128("0.9260761562750713360156803177935379") }
Because angle is stored as a 128-bit decimal, the $tanh output is also a 128-bit decimal.