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$atan
New in version 4.2.在版本4.2中新增。
Returns the inverse tangent (arc tangent) of a value.返回值的反切线（反正切）。
$atan has the following syntax:语法如下：
{ $atan: <expression> }
$atan takes any valid expression that resolves to a number.接受解析为数字的任何有效表达式。
$atan returns values in radians. 返回以弧度为单位的值。Use 使用$radiansToDegrees operator to convert the output value from radians to degrees.$radiansToDegrees运算符将输出值从弧度转换为度。
By default 默认情况下，$atan returns values as a double. $atan以double返回值。$atan can also return values as a 128-bit decimal as long as the <expression> resolves to a 128-bit decimal value.<expression>解析为128位十进制值，$atan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。
nullNaNIf the argument resolves to a value of 如果参数解析为null or refers to a field that is missing, $atan returns null. null值或引用缺少的字段，$atan将返回null值。If the argument resolves to 如果参数解析为NaN, $tan returns NaN.NaN，$tan返回NaN。
{ $atan: NaN } | NaN |
{ $atan: null } | null |
The trigonometry collection contains a document that
stores three sides of a right-angle triangle:
{
"_id" : ObjectId("5c50782193f833234ba90d85"),
"side_a" : NumberDecimal("3"),
"side_b" : NumberDecimal("4"),
"hypotenuse" : NumberDecimal("5")
}The following aggregation operation uses the
$atan expression to calculate the angle adjacent
to side_a and add it to the input document using the
$addFields pipeline stage.
db.trigonometry.aggregate([
{
$addFields : {
"angle_a" : {
$radiansToDegrees : {
$atan : {
$divide : [ "$side_b", "$side_a" ]
}
}
}
}
}
])The $radiansToDegrees expression converts the
radian value returned by $atan to the equivalent
value in degrees.
The command returns the following output:
{
"_id" : ObjectId("5c50782193f833234ba90d85"),
"side_a" : NumberDecimal("3"),
"side_b" : NumberDecimal("4"),
"hypotenuse" : NumberDecimal("5"),
"angle_a" : NumberDecimal("53.13010235415597870314438744090658")
}Since side_b and side_a are stored as
128-bit decimals, the output of
$atan is a 128-bit decimal.
The trigonometry collection contains a document that
stores three sides of a right-angle triangle:
{
"_id" : ObjectId("5c50782193f833234ba90d85"),
"side_a" : NumberDecimal("3"),
"side_b" : NumberDecimal("4"),
"hypotenuse" : NumberDecimal("5")
}The following aggregation operation uses the
$atan expression to calculate the angle adjacent
to side_a and add it to the input document using the
$addFields pipeline stage.
db.trigonometry.aggregate([
{
$addFields : {
"angle_a" : {
$atan : {
$divide : [ "$side_b", "$side_a" ]
}
}
}
}
])The command returns the following output:
{
"_id" : ObjectId("5c50782193f833234ba90d85"),
"side_a" : NumberDecimal("3"),
"side_b" : NumberDecimal("4"),
"hypotenuse" : NumberDecimal("5"),
"angle_a" : NumberDecimal("0.9272952180016122324285124629224287")
}Since side_b and side_a are stored as
128-bit decimals, the output of
$atan is a 128-bit decimal.