The Generalized Maximum Angle Condition for the Q1 Isoparametric Element

Abstract

We consider the quadrilateral $Q$₁ isoparametric element and establish an optimal error estimate in $H$¹ norm for the interpolation operator under a weaker mesh condition which admits anisotropic quadrilaterals and allows the quadrilateral to become a regular triangle in the sense of maximum angle condition [5,11].