General matrices

Question

I want to use LaTeX to add matrix that looks like this:

-----L_1-----

-----L_2-----

. . . . . . .

----L_n-----

and matrices where I want to show how a general cell in the matrix looks like (for example writing a matrix and then marking that 3 belongs to the i'th row and j'th column) , like here :

(I am not looking to a way to add the vertical lines ,but I want to have a matrix filled with dots, except at the i,j place and there write $2^{i+j}$ [ I want a matrix that each cell has the value of 2^{row number +column number})

Answer 1

For the first problem, look at Long dashes for denoting omitted columns of a matrix

For the second problem, the result will not be pretty:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\begin{pmatrix}
\makebox[9em]{\dotfill} \\
\makebox[9em]{\dotfill} \\
\makebox[9em]{\dotfill\ $2^{i+j}$ \dotfill} \\
\makebox[9em]{\dotfill} \\
\makebox[9em]{\dotfill} \\
\end{pmatrix}
\]

\end{document}

I'd very much prefer a simpler description:

The matrix $A=(a_{ij})$ where $a_{ij}=2^{i+j}$, for $1\le i,j\le n$