diff --git a/src/nodes2dofs.m b/src/nodes2dofs.m
new file mode 100644
index 0000000..b2ffe86
--- /dev/null
+++ b/src/nodes2dofs.m
@@ -0,0 +1,28 @@
+% Copyright (C) 2021, Jorge M. Perez Zerpa, J. Bruno Bazzano, Joaquin Viera,
+%   Mauricio Vanzulli, Marcelo Forets, Jean-Marc Battini, Sebastian Toro  
+%
+% This file is part of ONSAS.
+%
+% ONSAS 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 3 of the License, or
+% (at your option) any later version.
+%
+% ONSAS 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 ONSAS.  If not, see <https://www.gnu.org/licenses/>.
+
+% Function that converts a vector of nodes indices to a vector of the
+% corresponding degrees of freedom.
+
+function [dofs] = nodes2dofs( nodes , degreespernode )
+nodes= nodes(:) ;
+n    = length(nodes);
+dofs = zeros( n*degreespernode , 1 ) ;
+for i=1:n
+  dofs( (i-1)*degreespernode + (1:degreespernode) ) = [ (degreespernode*(nodes(i)-1))+(1:degreespernode) ]' ;
+end
diff --git a/tex/Cap2_NonLinGeo.tex b/tex/Cap2_NonLinGeo.tex
index c9e5549..94cef4d 100644
--- a/tex/Cap2_NonLinGeo.tex
+++ b/tex/Cap2_NonLinGeo.tex
@@ -1003,7 +1003,7 @@ \subsection{Método de los Elementos Finitos en análisis lineal de reticulados}
 %
 \begin{equation}
 \delta W_{\text{int}}(\bfu^e) %
-= \int_{\ell_0^e}  \delta \varepsilon^e \, \sigma^e \, \dif x %
+= \int_{\ell_0^e}  \delta \varepsilon^e \, \sigma^e \, A \, \dif x %
 %
 = \int_{\ell_0^e} \left( \delta \bfu^e\right)^{\text{T}} \left( \bfb_L^e\right)^{\text{T}} E A \bfb_L^e \bfu^e \, \dif x  %
 %
diff --git a/tex/libroANLE.pdf b/tex/libroANLE.pdf
index f2e9f62..8721a42 100644
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