generate weighted incidence matrix

Hello, how can I generate a random weighted incidence matrix? Something like this:

     3     4     0     0     0     0     0     0
    -3     0     1     1     7     0     0     0
     0     0    -1     0     0     3     0     0
     0    -4     0    -1     0     0     5     0
     0     0     0     0    -7     0    -5     6
     0     0     0     0     0    -3     0    -6

And how can I specify them,for example if the number of nodes, the density or the maximum weight is given?

My current solution looks like this:

    function [Inc] = randin(n, den, w)
    %generated random weighted incidence matrix for a directed graph with
    %n nodes, arc denisty den and maximal weight w 

    m=round(n*n*den); %calculate number of arcs
    Inc=zeros(n, m);
    for i=1:m
    c=randperm(w,1);  %calculate random weight
    d=randperm(n,1); %determines incoming/outgoing nodes
    e=randperm(n,1);
    while e==d       %incoming/outgoing nodes can not be the same
    e=randperm(n,1);
    endwhile
    Inc(d,i)=c;
    Inc(e,i)=-c;
    endfor
    Inc=sparse(Inc);
    endfunction

But I guess this is not a very efficient way to solve the problem, is it?

Thank you :)