Blaschke product

In complex analysis, the Blaschke product is a bounded analytic function in the open unit disc constructed to have zeros at a (finite or infinite) sequence of prescribed complex numbers

${\displaystyle a_{0},\ a_{1},\ldots }$

inside the unit disc, with the property that the magnitude of the function is constant along the boundary of the disc.

Blaschke products were introduced by Wilhelm Blaschke (1915). They are related to Hardy spaces.