Database Manual / Reference / Query Language / Expressions

$acosh (expression operator)（表达式运算符）

$acosh

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:具有以下语法：

{ $acosh: <expression> }

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

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

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

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, $acosh returns null. 如果参数解析为null值或引用缺少的字段，则$acosh将返回null。If the argument resolves to NaN, $acosh returns NaN. 如果参数解析为NaN，$acosh将返回NaN。If the argument resolves to negative infinity, $acosh throws an error. 如果参数解析为-Infinity，$acosh将抛出错误。If the argument resolves to Infinity, $acosh returns Infinity. 如果参数解析为Infinity，则$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将抛出错误。

Example示例Results结果
{ $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

Inverse Hyperbolic Cosine in Degrees以度为单位的逆双曲余弦

The trigonometry collection contains a document that stores a value along the x axis of a 2-D graph:trigonometry（三角学）集合包含一个文档，该文档存储了沿二维图x轴的值：

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : Decimal128("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 $addFields pipeline stage.以下聚合操作使用$acosh表达式计算x-coordinate的反双曲余弦，并使用$addFields管道阶段将其添加到输入文档中。

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

The $radiansToDegrees expression converts the radian value returned by $acosh to the equivalent value in degrees.$radiansToDegrees表达式将$acosh返回的弧度值转换为以度为单位的等效值。

The command returns the following output:该命令返回以下输出：

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : Decimal128("3"),
  "y-coordinate" : Decimal128("100.9979734210524228844295260083432")
}

Since x-coordinate is stored as a 128-bit decimal, the output of $acosh is a 128-bit decimal.由于x-coordinate存储为128位十进制，因此$acosh的输出是128位十进制。

Inverse Hyperbolic Cosine in Radians以弧度为单位的逆双曲余弦

The trigonometry collection contains a document that stores a value along the x axis of a 2-D graph:trigonometry集合包含一个文档，该文档存储了沿二维图x轴的值：

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : Decimal128("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 $addFields pipeline stage.以下聚合操作使用$acosh表达式计算x-coordinate的反双曲余弦，并使用$addFields管道阶段将其添加到输入文档中。

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

The command returns the following output:该命令返回以下输出：

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "x-coordinate" : Decimal128("3"),
  "y-coordinate" : Decimal128("1.762747174039086050465218649959585")
}

Since x-coordinate is stored as a 128-bit decimal, the output of $acosh is a 128-bit decimal.由于x-coordinate存储为128位十进制，因此$acosh的输出是128位十进制。