Weighted $\ell_q$ approximation problems on the ball and on the sphere

Let $L{q,\mu},\, 1\le q<\infty, \ \mu\ge0,$ denote the weighted $Lq$ space with the classical Jacobi weight $w\mu$ on the ball $\Bbb B^d$. We consider the weighted least $\ellq$ approximation problem for a given $L{q,\mu}$-Marcinkiewicz-Zygmund family on $\Bbb B^d$. We obtain the weighted least $\ellq$ approximation errors for the weighted Sobolev space $W{q,\mu}^r$, $r>(d+2\mu)/q$, which are order optimal. We also discuss the least squares quadrature induced by an $L{2,\mu}$-Marcinkiewicz-Zygmund family, and get the quadrature errors for $W{2,\mu}^r$, $r>(d+2\mu)/2$, which are also order optimal. Meanwhile, we give the corresponding the weighted least $\ellq$ approximation theorem and the least squares quadrature errors on the sphere.