Commit f1879960 authored by Björn Brandenburg's avatar Björn Brandenburg

add prefix_map transformation and two supporting lemmas

parent bf4412d0
From mathcomp Require Import ssrnat ssrbool fintype.
From rt.restructuring.behavior Require Import schedule facts.all.
(** This file provides an operation that transforms a finite prefix of
a given schedule by applying a point-wise transformation to each
instant up to a given horizon. *)
Section SchedulePrefixMap.
(* For any type of jobs and... *)
Context {Job : JobType}.
(* ... any given type of processor states ... *)
Context {PState: eqType}.
Context `{ProcessorState Job PState}.
(* ... we define a procedure that applies a given function to every
point in a given finite prefix of the schedule.
The point-wise transformation f is given a schedule and the point
to transform, and must yield a transformed schedule that is used
in subsequent operations. *)
Fixpoint prefix_map
(sched: schedule PState)
(f: schedule PState -> instant -> schedule PState)
(horizon: instant) :=
match horizon with
| 0 => sched
| S t =>
let
prefix := prefix_map sched f t
in f prefix t
end.
(** We provide a utility lemma that establishes that, if the
point-wise transformation maintains a given property of the
original schedule, then the prefix_map does so as well. *)
Section PropertyPreservation.
(* Given any property of schedules... *)
Variable P: schedule PState -> Prop.
(* ...and a point-wise transformation [f],... *)
Variable f: schedule PState -> instant -> schedule PState.
(* ...if [f] maintains property [P],... *)
Hypothesis H_f_maintains_P: forall sched t, P sched -> P (f sched t).
(* ...then so does a prefix map of [f]. *)
Lemma prefix_map_property_invariance:
forall sched h, P sched -> P (prefix_map sched f h).
Proof.
move=> sched h P_sched.
induction h; first by rewrite /prefix_map.
rewrite /prefix_map -/prefix_map.
by apply: H_f_maintains_P.
Qed.
End PropertyPreservation.
(** Next, we consider the case where the point-wise transformation
establishes a new property step-by-step. *)
Section PointwiseProperty.
(* Given any property of schedules [P],... *)
Variable P: schedule PState -> Prop.
(* ...any point-wise property [Q],... *)
Variable Q: schedule PState -> instant -> Prop.
(* ...and a point-wise transformation [f],... *)
Variable f: schedule PState -> instant -> schedule PState.
(* ...if [f] maintains [P]... *)
Hypothesis H_f_maintains_P:
forall sched t_ref,
P sched -> P (f sched t_ref).
(* ...and establishes [Q] (provided that [P] holds)... *)
Hypothesis H_f_grows_Q:
forall sched t_ref,
P sched ->
(forall t', t' < t_ref -> Q sched t') ->
forall t', t' <= t_ref -> Q (f sched t_ref) t'.
(* ...then the prefix-map operation will "grow" [Q] up to the horizon. *)
Lemma prefix_map_pointwise_property:
forall sched horizon,
P sched ->
forall t,
t < horizon ->
Q (prefix_map sched f horizon) t.
Proof.
move=> sched h P_holds.
induction h as [|h Q_holds_before_h]; first by rewrite /prefix_map.
rewrite /prefix_map -/prefix_map => t.
rewrite ltnS => LE_t_h.
apply H_f_grows_Q => //.
by apply prefix_map_property_invariance.
Qed.
End PointwiseProperty.
End SchedulePrefixMap.
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