/usr/share/octave/packages/bim-1.1.5/bim2a_boundary_mass.m is in octave-bim 1.1.5-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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##
## This file is part of:
## BIM - Diffusion Advection Reaction PDE Solver
##
## BIM is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## BIM is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with BIM; If not, see <http://www.gnu.org/licenses/>.
##
## author: Carlo de Falco <cdf _AT_ users.sourceforge.net>
## author: Massimiliano Culpo <culpo _AT_ users.sourceforge.net>
## -*- texinfo -*-
## @deftypefn {Function File} {[@var{M}]} = @
## bim2a_boundary_mass(@var{mesh},@var{sidelist},@var{nodelist})
##
## Build the lumped boundary mass matrix needed to apply Robin boundary
## conditions.
##
## The vector @var{sidelist} contains the list of the side edges
## contributing to the mass matrix.
##
## The optional argument @var{nodelist} contains the list of the
## degrees of freedom on the boundary.
##
## @seealso{bim2a_rhs, bim2a_advection_diffusion, bim2a_laplacian,
## bim2a_reaction}
## @end deftypefn
function [M] = bim2a_boundary_mass(mesh,sidelist,nodelist)
## Check input
if nargin > 3
error("bim2a_boundary_mass: wrong number of input parameters.");
elseif !(isstruct(mesh) && isfield(mesh,"p") &&
isfield (mesh,"t") && isfield(mesh,"e"))
error("bim2a_boundary_mass: first input is not a valid mesh structure.");
elseif !( isvector(sidelist) && isnumeric(sidelist) )
error("bim2a_boundary_mass: second input is not a valid numeric vector.");
endif
if nargin<3
[nodelist] = bim2c_unknowns_on_side(mesh,sidelist);
endif
edges = [];
for ie = sidelist
edges = [ edges, mesh.e([1:2 5],mesh.e(5,:)==ie)];
endfor
l = sqrt((mesh.p(1,edges(1,:))-mesh.p(1,edges(2,:))).^2 +
(mesh.p(2,edges(1,:))-mesh.p(2,edges(2,:))).^2);
dd = zeros(size(nodelist));
for in = 1:numel (nodelist)
dd (in) = (sum(l(edges(1,:)==nodelist(in)))+sum(l(edges(2,:)==nodelist(in))))/2;
endfor
M = sparse(diag(dd));
endfunction
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