Geopotential Note: A symbol for the empty set, , resembles Φ but is not Φ. or represents: the golden ratio 1.618... in mathematics, art, and architecture Euler's totient function in number theory the argument of a complex number in mathematics the value of a plane angle in physics and mathematics the angle to the z axis in spherical coordinates (mathematics) epoch or phase difference between two waves or vectors the angle to the x axis in the xy-plane in spherical or cylindrical coordinates (physics) latitude in geodesy radiant flux neutron flux electric potential a scalar field in quantum field theory the probability density function of the normal distribution in statistics the Veblen functions Χχ (chi) represents: the chi distribution in statistics ( is the more frequently encountered chi-squared distribution) the chromatic number of a graph in graph theory the Euler characteristic in algebraic topology electronegativity in the periodic table the Fourier transform of a linear response function a character in mathematics; especially a Dirichlet character in number theory sometimes the mole fraction a characteristic or indicator function in mathematics the magnetic susceptibility of a material in physics the fission neutron energy spectrum in neutron transport Ψψ (psi) Ψ represents: water potential a quaternary combinator in combinatory logic a symbol for psychology represents: the wave function in the Schrödinger equation of quantum mechanics the psi-Mesons in particle physics the stream function in fluid dynamics the reciprocal Fibonacci constant the second Chebyshev function in number theory the polygamma function in mathematics the supergolden ratio Ωω (omega) Ω represents: Absolute Infinity the SI unit measure of electrical resistance, the ohm the right ascension of the ascending node (RAAN) or Longitude of the ascending node in astronomy and orbital mechanics the omega constant 0.5671432904097838729999686622... an asymptotic lower bound notation related to big O notation in probability theory and statistical mechanics, the support a solid angle the omega baryon the arithmetic function counting a number's prime factors counted with multiplicity the density parameter in cosmology the first uncountable ordinal (also written as ω1) represents: angular velocity / radian frequency (rad/sec) the argument of periapsis in astronomy and orbital mechanics a complex cube root of unity — the other is — (used to describe various ways of calculating the discrete Fourier transform) the differentiability class (i.e. ) for functions that are infinitely differentiable because they are complex analytic the first infinite ordinal the omega meson the