Let $p,qin mathbf{R}ackslash {0}$ and $A=(a_{n,k})_{n,kgeq0}$ be a non-negative matrix. Denote by $L_{p,q}(A)$ the supremum of those $L$ satisfying the following inequality: $$ left(sum_{n=0}^inftyleft(sum_{k=0}^infty a_{n,k}x_k ight)^q ight)^{1/q}geq Lleft(sum_{k=0}^infty {x_k}^p ight)^{1/p}qquad(Xin ell_p, Xge 0).$$ The purpose of this thesis is to find the exact value of $L_{p,q}(A)$ for summability matrices, Hausdorff matrices, weighted mean matrices, N"orlund matrices, and their transposes, where $0