# Vector:Dot

number Vector:Dot( Vector otherVector )

# Description

Returns the dot product of this vector and the passed one.

The dot product of two vectors is the product of their magnitudes (lengths), and the cosine of the angle between them:

a · b = |a| |b| cos(θ)

where a and b are vectors.

See Vector:Length for obtaining magnitudes.

A dot product returns just the cosine of the angle if both vectors are normalized, and zero if the vectors are at right angles to each other.

# Arguments

1 Vector otherVector
The vector to calculate the dot product with

# Returns

1 number
The dot product between the two vectors

## Example

Get the angle of two opposite normalized vectors.

local a = Vector(0, 1, 0) local b = Vector(0, -1, 0) local dot = a:Dot(b) -- returns the cos(ang) of the two vectors because they're both of length 1 print("Radians", math.acos(dot)) -- the inverse of the cosine to get the angle print("Degrees", math.deg(math.acos(dot))) -- Convert radians to degrees
Degrees 180

## Example

Calculates whether the player is looking in the direction of an entity. This is often faster than traces, but it produces a slightly different result.

The player is looking in the direction of the entity if the angle between the aimvector and the vector from the player to the entity is less than 22.5 degrees (or pi / 8 radians).

local directionAngCos = math.cos(math.pi / 8) local aimVector = ply:GetAimVector() -- The vector that goes from the player's shoot pos to the entity's position local entVector = ent:GetPos() - ply:GetShootPos() local angCos = aimVector:Dot(entVector) / entVector:Length() print(angCos >= directionAngCos)
Output: This script will say if the player is looking in the direction of the entity.

## Example

A function to make sure the player is looking somewhere.

function IsLookingAt(ply, targetVec) local diff = targetVec - ply:GetShootPos() return ply:GetAimVector():Dot(diff) / diff:Length() >= 0.95 end
Output: Returns true if ply is looking at (or close to) the target.