phi: the golden ratio

phi is the golden ratio, (1 + √5)/2, approximately 1.618034. It occurs in algebraic identities, geometry, and some recursive sequences.

Use

Use sqrt() to construct its exact form and pow() in its identities. Compare it to pi as another important dimensionless constant, and use numeric() for decimals.

Caveat

Its aesthetic reputation does not make it a universal design rule; use it where the mathematics actually applies.