In MongoDB, the $cosh aggregation pipeline operator returns the hyperbolic cosine of a value that is measured in radians.

$cosh accepts any valid expression that resolves to a number.

The $cosh operator was introduced in MongoDB 4.2.

Example

Suppose we have a collection called test with the following document:

{ "_id" : 1, "data" : 3 }

We can use the $cosh operator to return the cosine of the data field:

db.test.aggregate(
  [
    { $match: { _id: 1 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: "$data" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : 10.067661995777765 }

By default, the $cosh operator returns values as a double, but it can also return values as a 128-bit decimal as long as the expression resolves to a 128-bit decimal value.

When the Expression is in Degrees

As mentioned, $cosh accepts its expression in radians. You can use the $degreesToRadians operator to convert any values from degrees to radians.

Example:

db.test.aggregate(
  [
    { $match: { _id: 1 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $degreesToRadians: { $cosh: "$data" } }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : 0.17571384980422547 }

Null Values

Null values return null when using the $cosh operator.

Suppose we add the following document to our collection:

{ "_id" : 3, "data" : null }

Let’s run the the $cosh operator against that document:

db.test.aggregate(
  [
    { $match: { _id: 3 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: "$data" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : null }

We can see that the result is null.

NaN Values

If the argument resolves to NaN, $cosh returns NaN.

Example:

db.test.aggregate(
  [
    { $match: { _id: 3 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: 1 * "string" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : NaN }

In this case I tried to multiple a number by a string, which resulted in NaN being returned.

Infinity

If the argument resolves to Infinity or -Infinity, the $cosh operator returns Infinity.

Suppose we add the following document to our collection:

{ "_id" : 4, "data" : Infinity }

Let’s run $cosh against the data field:

db.test.aggregate(
  [
    { $match: { _id: 4 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: "$data" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : Infinity }

Non-Existent Fields

If the $cosh operator is applied against a field that doesn’t exist, null is returned.

Example:

db.test.aggregate(
  [
    { $match: { _id: 4 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: "$name" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : null }

128-bit Decimal

As mentioned, if the expression provided to $cosh is 128-bit decimal, then the result is returned in 128-bit decimal.

Suppose we add the following document to the collection:

{ "_id" : 5, "data" : NumberDecimal("1.1301023541559787031443874490659") }

Here’s what happens when we run that through the $cosh operator:

db.test.aggregate(
  [
    { $match: { _id: 5 } },
    { $project: { 
        _id: 0,
        hyperbolicCosine: { $cosh: "$data" }
      }
    }
  ]
)

Result:

{ "hyperbolicCosine" : NumberDecimal("1.709486781983575502518713909095045") }

The output is 128-bit decimal.