R - atan2() Function

The R atan2() function returns the angle theta from the conversion of rectangular coordinates (x, y) to polar coordinates (r, theta). The returned value will be in the range -𝜋 through 𝜋. In special cases it returns the following:

• If either argument is NaN, then the result is NaN.
• If both arguments are positive infinity, then the result is closest to 𝜋/4.
• If the first argument is positive or negative finite and the second argument is positive infinity, then the result is zero.
• If the first argument is positive or negative finite and the second argument is negative infinity, then the result is closest to 𝜋.
• If the first argument is positive and the second argument is zero, or the first argument is positive infinity and the second argument is finite, then the result is closest to 𝜋/2.
• If the first argument is negative and the second argument is zero, or the first argument is negative infinity and the second argument is finite, then the result is closest to -𝜋/2.
• If the first argument is positive infinity and the second argument is negative infinity, then the result is closest to 3*𝜋/4.
• If the first argument is negative infinity and the second argument is positive infinity, then the result is closest to -𝜋/4.
• If both arguments are negative infinity, then the result is closest to -3*𝜋/4.

Syntax

atan2(y, x)

Parameters

Return Value

Returns theta of the point (r, theta) in polar coordinates that corresponds to the point (x, y) in Cartesian coordinates.

Example:

In the example below, atan2() function is used to calculate the theta of a point.

#operating on single element atomic vectors
print(atan2(10, 10))
print(atan2(0, 10))
print(atan2(-10, 10))
print(atan2(-10, -10))

cat("\nOperating on vectors\n")
#operating on vectors
v1 <- c(0, 10, Inf)
v2 <- c(10, 20, -Inf)
print(atan2(v1, v2))

cat("\nOperating on matrices\n")
#operating on matrices
m1 <- matrix(c(-2, Inf, 10, -10, Inf, NaN), nrow=2)
m2 <- matrix(c(2, NaN, 20, 20, 0, NaN), nrow=2)
print(atan2(m1, m2))

cat("\nOperating on first column of matrices\n")
#operating on first column of matrices
print(atan2(m1[,1], m2[,1]))

The output of the above code will be:

[1] 0.7853982
[1] 0
[1] -0.7853982
[1] -2.356194

Operating on vectors
[1] 0.0000000 0.4636476 2.3561945

Operating on matrices
           [,1]       [,2]     [,3]
[1,] -0.7853982  0.4636476 1.570796
[2,]        NaN -0.4636476      NaN

Operating on first column of matrices
[1] -0.7853982        NaN