Variation diminishing properties of Bernstein polynomials on triangles

Abstract We show that if f is any function on a triangle T, then the variation of the gradient of the nth Bernstein polynomial Bn(f) on T cannot exceed the variation of the gradient of the nth Bezier net \ tf n on T. We deduce that if f is in C2(T), then the variation of the gradient of Bn(f) on T is bounded by a given constant (depending on T) times the variation of the gradient of f. It is further shown that the variation of Bn(f) on T is bounded by 2n (n + 1) times the variation of \ tf n on T.