NAME
    atan - arc tangent

SYNOPSIS
    atan(x [,acc])

TYPES
    x		real
    acc		real

    return	real

DESCRIPTION
    Calculate the arc tangent of x with an accuracy within eps.
    By default, eps is epsilon().

    The arc tangent is calculated using the formula:

	atan(x) = asin(sqrt(x^2 / (x^2 + 1)))

EXAMPLE
    > print atan(0), atan(1-2^36), 1e-4), atan(1-2^106, 1e-100)
    0 ~-1.57079632677946198232 ~-1.57079632679489661923

LIMITS
    acc > 0

LIBRARY
    NUMBER *qatan(NUMBER *x, *acc)

SEE ALSO
    acos, asin, atan2, cos, epsilon, sin, tan
