To resample all random parameters, you can also use reset data
followed by whatever data statements are necessary to re-read the
non-random parameter data.

> As discussed below, with AMPL versions prior to 19951020, you must use
> default rather than := in declaring param avail:
> 
		param avail {s in STAGE} default 
			Normal (avail_mean[s], avail_var[s]);

305a337,421
> There are some subtleties:
>   1.  AMPL does not evaluate default and := expressions until they are
> needed, so the sequence of commands you issue can affect the random
> values it computes.
>   2.  If p is an indexed parameter that lacks a := expression,
> "display p;" only shows the components of p that have been read,
> assigned by "let", or computed when necessary from a default expression.
> Thus if p has a default expression, "display p;" may show nothing until
> some other command forces some components of p to be computed.  On the
> other hand, any reference to an indexed parameter with a := expression
> causes all of its components to be computed.  For example:
> 
> 		ampl: set A;
> 		ampl: param p{A};
> 		ampl: param q{A} default Uniform01();
> 		ampl: param r{i in A} := q[i] + 1;
> 		ampl: data; set A := a b c d;
> 		ampl data: param  p := a 1.3  d 2.7;
> 		ampl data: display p,q;   # no values for q yet
> 		:    p   q    :=
> 		a   1.3   .
> 		d   2.7   .
> 		;
> 		
> 		ampl: display r;	# Force q to be computed.
> 		r [*] :=
> 		a  1.60921
> 		b  1.18987
> 		c  1.92189
> 		d  1.95716
> 		;
> 		
> 		ampl: display p,q,r;
> 		:    p       q          r       :=
> 		a   1.3   0.609209   1.60921
> 		b    .    0.189873   1.18987
> 		c    .    0.921892   1.92189
> 		d   2.7   0.957156   1.95716
> 		;
> 
>   3.  Parameters declared with a := expression, even one that involves
> a random function, are only recomputed after a set or parameter on which
> they depend has changed.  AMPL versions earlier than 19951020 would
> complain at
> 
> 		param p := Uniform01();
> 		reset data p;
> 
> complaining that "p has a := value in the model", and would not
> resample p after a "reset data;" command.  Starting with version
> 19951020, "reset data p;" and "reset data;" cause p to be resampled.
> With the earlier versions, it is safest to use default expressions rather
> than := expressions for random-valued parameters.  For example (with
> an earlier version):
> 
> 		ampl: param p := Uniform01();
> 		ampl: param q default Uniform01();
> 		ampl: set I default 1..3;
> 		ampl: param r{I} := Uniform01();
> 		ampl: param s{1..3} := Uniform01();
> 		ampl: display p,q,r,s;
> 		p = 0.609209
> 		q = 0.263135
> 		
> 		:      r          s        :=
> 		1   0.189873   0.105726
> 		2   0.921892   0.714106
> 		3   0.957156   0.551532
> 		;
> 		
> 		ampl: reset data;
> 		ampl: display p,q,r,s;
> 		p = 0.609209
> 		q = 0.575807
> 		
> 		:      r          s        :=
> 		1   0.349604   0.105726
> 		2   0.407247   0.714106
> 		3   0.665212   0.551532
> 		;
> 
> Notice that p and s were not affected by "reset data;".
> Parameter r was recomputed because "reset data;" forced
> its index set to be recomputed.
>