Support AMPL files

The following files are useful for several discretized control problems listed on the AMPL Category page. They need to be saved to the same directory.

ampl_general.mod

param T    > 0;     # End time
param nt   > 0;     # Number of discretization points in time
param nu   > 0;     # Number of control discretization points
param nx   > 0;     # Dimension of differential state vector
param ntperu > 0;   # nt / nu
set I:= 0..nt;
set U:= 0..nu-1;
param uidx {I}; param fix_w; param fix_w;

var w {U} >= 0, <= 1 binary;    # control function
var dt {U} >= 0, <= T;          # stage length vector

ampl_general.dat

if ( fix_w > 0 )  then { for {i in U} { fix w[i]; } }
if ( fix_dt > 0 ) then { for {i in U} { fix dt[i]; } }

# Set indices of controls corresponding to time points
for {i in 0..nu-1} {
  for {j in 0..ntperu-1} { let uidx[i*ntperu+j] := i; }
}
let uidx[nt] := nu-1;