Database Manual / Reference / Query Language / Expressions

$tanh (expression operator)

$tanh

Returns the hyperbolic tangent of a value that is measured in radians.

$tanh has the following syntax:

{ $tanh: <expression> }

$tanh takes any valid expression that resolves to a number, measured in radians. If the expression returns a value in degrees, use the $degreesToRadians operator to convert the value to radians.

By default $tanh returns values as a double. $tanh can also return values as a 128-bit decimal if the <expression> resolves to a 128-bit decimal value.

For more information on expressions, see Expressions.

Behavior

null, NaN, and +/- 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.

ExampleResults

{ $tanh: NaN }

NaN

{ $tanh: null }

null

{ $tanh: -Infinity }

-1

{ $tanh: Infinity }

1

Example

The following trigonometry collection contains a document that stores an angle value measured in degrees:

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" } }
      }
   }
] )

The $degreesToRadians expression converts the angle in degrees to radians.

Example output:

{
   "_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.

The following trigonometry collection contains a document that stores an angle value measured in radians:

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" }
      }
   }
] )

Example output:

{
   "_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.