This is the file .che that controls the behavior of CHE_EVO. 

The file consists of several sections, which can appear in any order and
begins with  a line consisting only in one of the following keywords.

- MAIN: section devoted to main parameters defining the model
- IMF: section where the IMF is specified.
When CHE_EVO is used coupled with GRASIL, there must be correspondence
between this IMF and that for which the SSPs libraries are computed
(but for small changes of the lower mass limit). 
- ANALY: section where the parameters defining the analytical component
of SFR are given. Used only if i_sfr_t<>0 in section MAIN.


section MAIN is 'free form': the parameters can appear in any order, each one
on a different line of the file. The line contains the name of the parameter
in the first ten columns, its value from column 11 to column 20, and the rest
of the line is left for comments. In addition, each line starting with %, # or
a blank space is ignored, and can be used for longer comments. The other
sections are instead fixed form and their structure (order of lines, order of
parameters in line, number of comment lines, etc..) can't be changed.


MAIN
# This section is quite free form: parameters may appear in any order,
# lines begining with #, % or blank space are for comments, otherwise
# from column 1 to 10 an identifier of the parameter (case sensitive)
# from 11 to 20 its value (always real with explicit decimal point)
# from 21 on comments.
#2345678901234567890123456789
#
t_fin     12.1      final galactic age
i_sfr_m   1.0       0->nothing, 1->simple Schmidt, 2->Talbot & Arnett
# set i_sfr_m = 0  to switch off the Schmidt type term of the SF 
# (i.e. to leave only analytical function of t)
i_sfr_t   1.0       0->nothing, 1->constant, 2->exponential
# set i_sfr_t =0 to switch off the analytical term of the SF 
# (i.e. to leave only the function of Mgas)
t_win     100.0     age at which any sf is stopped (see olso the note on t_inf)
f_win     1.8e-3    after t_win the feed-back rate is multiplied by f_win
k_sch     1.0       exponent of schmidt law
nu_sch    2.0       efficiency of schmidt law
tau_inf   0.1       exponential infall timescale
m_inf     1.e11     infall mass at t_inf  
#
# NOTE CAREFULLY: t_inf is reset internally to min(t_inf,t_win) !!
t_inf     1.0       see m_inf
int_flag  1.0       if 1.0 interpolates fbr internally to timesteps
# leave int_flag=1.0
m_up      8.0       minimum mass for SNII (used for SNR, not ejecta)
#


IMF
# Parameters for  IMF.
1
0.15 120.0
1.35
The integer in the first row of this section is the number of pieces n_imf of
the adopted power law IMF, the second row gives the boundaries of the pieces,
and must containg n_imf+1 real numbers. The third row has n_imf real numbers,
which are the exponents (in mass) of the IMF in each piece.

For instance, for a Salpeter IMF, n_imf=1, the second row has two numbers
the lower and upper limits of IMF (say 0.15 and 120.0, like in the SSP files),
and the third has the exponent 1.35

#
#
ANALY
# Parameters for SF dependent on t: t1_sfr_t, t2_sfr_t, fra_sfr_t, tau_sfr_t
12.95 13.0 0.0117 0.05
Meaning of the numbers in the above line:
t1_sfr_t: age at which analytical sft(t) onset
t2_sfr_t: age at which analytical sfr(t) is stopped
fra_sfr_t: mass converted to stars by analytical sfr(t) between the above ages
in units of m_inf given in section MAIN
tau_sfr_t: timescale for exponential sft(t) (used only fro i_sfr_m=1)