tested that input works

include/thermodynamics.h

@@ -151,6 +151,9 @@ struct thermo
   double annihilation_f_halo; /** takes the contribution of DM annihilation in halos into account*/
   double annihilation_z_halo; /** characteristic redshift for DM annihilation in halos*/
 
+  double u_nuDM;              /** DM-NU scattering cross section normalized to the Thomson cross
+				  section and a DM mass of 100 GeV */
+  short has_coupling_nuDM;   /** flag to indicate weather the scattering is present */
   //@}
 
   /** @name - all indices for the vector of thermodynamical (=th) quantities stored in table */
@@ -172,6 +175,7 @@ struct thermo
   int index_th_ddcb2;         /**< second derivative wrt conformal time of squared baryon sound speed  \f$ d^2 [c_b^2] / d \tau^2 \f$ (only computed if some non0-minimal tight-coupling schemes is requested) */
   int index_th_rate;          /**< maximum variation rate of \f$ exp^{-\kappa}\f$, g and \f$ (d g / d \tau) \f$, used for computing integration step in perturbation module */
   int index_th_r_d;           /**< simple analytic approximation to the photon comoving damping scale */
+  int index_th_dmu_nDM;       /**< rate for DM-neutrino scattering */
   int th_size;                /**< size of thermodynamics vector */
 
   //@}

nuDM.ini

+-----------------------------------------------------
+---> COSMOLOGICAL PARAMETERS
+---> planck best fit
+-----------------------------------------------------
+Omega_cdm    = 0.2644
+Omega_b      = 0.04909
+Omega_Lambda = 0.6851
+h            = 0.6731
+n_s          = 0.9658
+A_s          = 2.199e-9
+
+---------------------------------------------------
+---> NEUTRINOS
+---> two massless and one massiv neutrino of 0.06eV
+---> N_eff is 3.046
+----------------------------------------------------
+N_ur = 3.046
+#N_ur   = 2.0328
+#N_ncdm = 1
+#m_ncdm = 0.06
+#T_ncdm = 0.71611
+
+-------------------
+---> g-cdm coupling
+-------------------
+u_nuDM        = 0.01
+gauge         = newtonian
+k_pivot       = 0.05
+sBBN file     = ./bbn/sBBN.dat
+
+-----------
+---> OUTPUT
+-----------
+output               = tCl
+root                 = output/2018-10-17_implementation-testing/random-test
+format               = camb
+#k_per_decade_for_pk  = 100
+#P_k_max_h/Mpc        = 100.
+write parameters     = yes
+write background     = no
+write thermodynamics = no
+#k_output_values      = 
+
+-----------------------
+---> breake the silence
+-----------------------
+input_verbose          = 1
+background_verbose     = 1
+thermodynamics_verbose = 1
+perturbations_verbose  = 1
+transfer_verbose       = 1
+primordial_verbose     = 1
+spectra_verbose        = 1
+nonlinear_verbose      = 1
+lensing_verbose        = 1
+output_verbose         = 1