In mathematics, the epigraph or supergraph, denoted by epi ⁡ f, {\displaystyle \operatorname {epi} f,} of a function f {\displaystyle f} valued in the extended real numbers, f : X → [ − ∞, ∞ ] = R ∪ { ± ∞ } {\displaystyle f:X\to [-\infty,\infty ]=\mathbb {R} \cup \{\pm \infty \}}, is the set of all points in the Cartesian product X × R {\displaystyle X\times \mathbb {R} } lying on or above its graph. Wikipedia