Best polynomial approximation on the triangle

Han Feng, Christian Krattenthaler, Yuan Xu

Let $E_n(f{)}_{\alpha ,\beta ,\gamma }$ denote the error of best approximation by polynomials of degree at most $n$ in the space $L^2({\varpi }_{\alpha ,\beta ,\gamma })$ on the triangle $\{(x,y): x, y \ge 0, x+y \le 1\…