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$atanh (aggregation)

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$atanh

New in version 4.2.

Returns the inverse hyperbolic tangent (hyperbolic arc tangent) of a value.

$atanh has the following syntax:

{ $atanh: <expression> }

$atanh takes any valid expression that resolves to a number between -1 and 1, e.g. -1 <= value <= 1.

$atanh returns values in radians. Use $radiansToDegrees operator to convert the output value from radians to degrees.

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

For more information on expressions, see Expressions.

Behavior

null, NaN, and +/- Infinity

If the argument resolves to a value of null or refers to a field that is missing, $atanh returns null. If the argument resolves to NaN, $atanh returns NaN. If the argument resolves to negative or positive infinity, $atanh throws an error. If the argument resolves to +1 or -1, $atanh returns Infinity and -Infinity respectively.

ExampleResults
{ $atanh: NaN }NaN
{ $atanh: null }null
{ $atanh: 1 }Infinity
{ $atanh: -1}-Infinity
{ $atanh : Infinity}
or
{ $atanh : -Infinity } 		Throws an error message resembling the following formatted output: 
"errmsg" :
  "Failed to optimize pipeline :: caused by :: cannot
  apply $atanh to -inf, value must in (-inf,inf)"

Example