No need for a dept command, use beamer institute command instead

Makefile

-TOP = model.pdf
+TOP ?= model.pdf
 
 FIGS       = $(wildcard figs/*.fig)
 FIGS_PDF   = $(patsubst %.fig,%.pdftex,$(FIGS))

model.tex

@@ -54,8 +54,7 @@
 \subtitle{model}
 
 \author{Graba Tarik}
-\institute{ TELECOM ParisTech }
-\dept{COMELEC--SEN}
+\institute{COMELEC--SEN}
 \extralogo{\includegraphics[width=2cm]{logo-cnrs}}
 \date{}
 %------------------------------------------------------------------------------

texinputs/beamerthemetptnew.sty

@@ -184,7 +184,7 @@
       \hfill{}%
       \begin{beamercolorbox}[wd=.27\paperwidth,ht=\footlineheight,dp=1.5ex,leftskip=1em,rightskip=1em]{dept in head/foot}%
          \hfill{}%
-         \usebeamerfont{dept in head/foot}\insertdept%
+         \usebeamerfont{dept in head/foot}\insertinstitute%
          \hfill{}\hfill{}%
       \end{beamercolorbox}%
       \hspace*{\footlinespacing}%