$acosh (aggregation)

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$acosh

New in version 4.2.在版本4.2中新增。

Returns the inverse hyperbolic cosine (hyperbolic arc cosine) of a value.返回值的反双曲余弦（双曲弧余弦）。

$acosh has the following syntax:语法如下：

{ $acosh: <expression> }

$acosh takes any valid expression that resolves to a number between 1 and +Infinity, e.g. 1 <= value <= +Infinity.$acosh接受任何有效表达式，该表达式解析为1到+Infinity之间的数字，例如1 <= value <= +Infinity。

$acosh returns values in radians. 返回以弧度为单位的值。Use $radiansToDegrees operator to convert the output value from radians to degrees.使用$radiansToDegrees运算符将输出值从弧度转换为度。

By default $acosh returns values as a double. 默认情况下，$acosh以double返回值。$acosh can also return values as a 128-bit decimal as long as the <expression> resolves to a 128-bit decimal value.只要<expression>解析为128位十进制值，也可以以128位十进制返回值。

For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

null, NaN, and +/- Infinity

If the argument resolves to a value of null or refers to a field that is missing, $acosh returns null. 如果参数解析为null值或引用缺少的字段，$acosh返回null。If the argument resolves to NaN, $acosh returns NaN. 如果参数解析为NaN，$acosh返回NaN。If the argument resolves to negative infinity, $acosh throws an error. 如果参数解析为负无穷大，$acosh抛出一个错误。If the argument resolves to Infinity, $acosh returns Infinity. 如果参数解析为Infinity，$acosh返回Infinity。If the argument resolves to a value outside the bounds of [-1, Infinity] inclusive, $acosh throws an error.如果参数解析为[-1, Infinity]范围之外的值，则$acosh抛出错误。

Example实例Results后果
{ $acosh: NaN }NaN
{ $acosh: null }null
{ $acosh : Infinity}Infinity
{ $acosh : 0 }

Throws an error message resembling the following formatted output:抛出类似以下格式化输出的错误消息：

"errmsg" :
  "Failed to optimize pipeline :: caused by :: cannot
  apply $acosh to -inf, value must in (1,inf)"

Example示例

The trigonometry collection contains a document that stores a value along the x axis of a 2-D graph:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : NumberDecimal("3")
}

The following aggregation operation uses the $acosh expression to calculate inverse hyperbolic cosine of x-coordinate and add it to the input document using the $addFields pipeline stage.

db.trigonometry.aggregate([
  {
    $addFields : {
      "y-coordinate" : {
        $radiansToDegrees : { $acosh : "$x-coordinate" }
      }
    }
  }
])

The $radiansToDegrees expression converts the radian value returned by $acosh to the equivalent value in degrees.

The command returns the following output:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : NumberDecimal("3"),
  "y-coordinate" : NumberDecimal("100.9979734210524228844295260083432")
}

Since x-coordinate is stored as a 128-bit decimal, the output of $acosh is a 128-bit decimal.

The trigonometry collection contains a document that stores a value along the x axis of a 2-D graph:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : NumberDecimal("3")
}

The following aggregation operation uses the $acosh expression to calculate inverse hyperbolic cosine of x-coordinate and add it to the input document using the $addFields pipeline stage.

db.trigonometry.aggregate([
  {
    $addFields : {
      "y-coordinate" : {
        $acosh : "$x-coordinate"
      }
    }
  }
])

The command returns the following output:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : NumberDecimal("3"),
  "y-coordinate" : NumberDecimal("1.762747174039086050465218649959585")
}

Since x-coordinate is stored as a 128-bit decimal, the output of $acosh is a 128-bit decimal.

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