srcAcc

function amat = srcAcc(i,j,val,bmat)
%srcAcc(i,j,val,bmat)
%   Accumulates Is or Vs values onto source matrix bmat.
%     Index i is "from" node (drop mesh).
%     Index j is "to" node (rise mesh).
if (j > 0)
    bmat(j)=bmat(j)+val;
end
if (i > 0)
    bmat(i)=bmat(i)-val;
end
amat=bmat;