Psi function

Psi function can refer, in mathematics, to
 * the ordinal collapsing function $$\psi(\alpha)$$
 * the Dedekind psi function $$\psi(n)$$
 * the Chebyshev function $$\psi(x)$$
 * the polygamma function $$\psi^m(z)$$ or its special cases
 * the digamma function $$\psi(z)$$
 * the trigamma function $$\psi^1(z)$$

and in physics to
 * the quantum mechanical wave function.