File size: 7,622 Bytes
9425aed
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
-- Loop Invariant: integrator_evolve
-- BOB Quantum Kernel β€” Time Evolution Main Loop
-- Phase 2: Formal Structure (no proofs yet)
-- WORM-sealed observable bookkeeping

module Invariants.EvolutionLoop where

open import Data.Nat using (β„•; _+_; _≀_; _<_; _β‰₯_; zero; suc)
open import Data.Real using (ℝ; _+_; _*_; _-_; _<_; _≀_; _β‰₯_)
open import Data.Bool using (Bool; true; false)
open import Relation.Binary.PropositionalEquality using (_≑_; refl; cong)
open import Core.ErrorCode using (ErrorCode; BOB_SUCCESS; isSuccess)
open import Core.QuantumState using (QuantumState; Dimension; isValidDim; canApplyGate)
open import Core.Hamiltonian using (Hamiltonian; isValidHamiltonian; hamiltonianImmutable)
open import Core.Predicates using (stepInRange; errorIsClear; needsNormalization; canContinueLoop; loopCompleted)

-- ============================================================================
-- Loop State: All variables captured at step k
-- ============================================================================

record EvolutionState : Set where
  field
    step : β„•                    -- iteration counter k ∈ [0, num_steps]
    state : QuantumState         -- quantum state (mutable, evolving)
    hamiltonian : Hamiltonian    -- time-independent operator (immutable)
    dt : ℝ                       -- time step (immutable, positive)
    num_steps : β„•                -- total iteration count (immutable)
    error_status : β„•             -- error code (0=BOB_SUCCESS, etc.)
    normalization_log : β„• β†’ Bool -- which steps were normalized?
    accumulated_time : ℝ         -- βˆ‘(dt for steps taken)

-- ============================================================================
-- Loop Invariant: Predicate over state and step count
-- ============================================================================

-- At each iteration k, what must be true?
record EvolutionInvariant (s : EvolutionState) (k : β„•) : Set where
  field
    -- 1. Step counter matches loop variable
    h_step_eq : EvolutionState.step s ≑ k

    -- 2. Error status is success (loop hasn't aborted)
    h_error : errorIsClear (EvolutionState.error_status s)

    -- 3. Quantum state is dimensionally valid
    h_state_valid : isValidDim (EvolutionState.state s)

    -- 4. Hamiltonian is valid
    h_ham_valid : isValidHamiltonian (EvolutionState.hamiltonian s)

    -- 5. Time step is positive
    h_dt_pos : EvolutionState.dt s > 0

    -- 6. Current step ≀ num_steps (loop guard)
    h_in_range : k ≀ EvolutionState.num_steps s

    -- 7. Accumulated time = k * dt
    h_accumulated_time :
      EvolutionState.accumulated_time s ≑ (ℝ.fromβ„• k) * (EvolutionState.dt s)

    -- 8. Normalization log: for each step m ≀ k, if m ≑ 0 (mod 100), then normalized
    h_norm_schedule :
      βˆ€ (m : β„•) β†’ m < k β†’ (m mod 100 ≑ 0) β†’ (EvolutionState.normalization_log s m ≑ true)

-- ============================================================================
-- Base Case: k = 0 (before loop starts)
-- ============================================================================

evolution_base :
  (s : EvolutionState) β†’
  EvolutionState.step s ≑ 0 β†’
  EvolutionState.error_status s ≑ 0 β†’
  isValidDim (EvolutionState.state s) β†’
  isValidHamiltonian (EvolutionState.hamiltonian s) β†’
  EvolutionState.dt s > 0 β†’
  EvolutionState.accumulated_time s ≑ 0 β†’
  EvolutionInvariant s 0

evolution_base s h_step h_error h_state_valid h_ham_valid h_dt_pos h_acc_time =
  record
    { h_step_eq = h_step
    ; h_error = h_error
    ; h_state_valid = h_state_valid
    ; h_ham_valid = h_ham_valid
    ; h_dt_pos = h_dt_pos
    ; h_in_range = Ξ» where
        0 β†’ zero
    ; h_accumulated_time = h_acc_time
    ; h_norm_schedule = Ξ» m h_lt_zero _ β†’ absurd (Β¬(<-zero m) h_lt_zero)
    }
  where
    Β¬(<-zero : βˆ€ n β†’ Β¬(n < 0)
    Β¬(<-zero _ ()

-- ============================================================================
-- Inductive Step: k β†’ k+1
-- ============================================================================

-- Represents one call to integrator_step(state, hamiltonian)
record StepTransition (s s' : EvolutionState) : Set where
  field
    -- Same invariant on input state
    pre_inv : EvolutionInvariant s (EvolutionState.step s)

    -- Step counter increments by 1
    step_increments : EvolutionState.step s' ≑ EvolutionState.step s + 1

    -- State changed (evolved one step)
    state_changed : EvolutionState.state s β‰  EvolutionState.state s'

    -- Hamiltonian unchanged
    ham_unchanged :
      (EvolutionState.hamiltonian s ≑ EvolutionState.hamiltonian s') ∨
      (hamiltonianImmutable (EvolutionState.hamiltonian s) (EvolutionState.hamiltonian s'))

    -- Quantum state remains valid-dimensioned after evolution (physics invariant)
    state_valid_preserved :
      isValidDim (EvolutionState.state s) β†’
      isValidDim (EvolutionState.state s')

    -- Error status either remains success or becomes error (and loop exits)
    error_inv : (EvolutionState.error_status s' ≑ 0) ∨
               (EvolutionState.error_status s' β‰  0)

    -- Accumulated time increases by dt
    time_advances :
      EvolutionState.accumulated_time s' ≑
      EvolutionState.accumulated_time s + EvolutionState.dt s

-- Inductive step: if invariant holds at k, then after one step it holds at k+1
-- (OR the loop exits due to error)
evolution_step :
  (s s' : EvolutionState) (k : β„•) β†’
  EvolutionInvariant s k β†’
  StepTransition s s' β†’
  -- If no error, then invariant holds at k+1
  (EvolutionState.error_status s' ≑ 0) β†’
  EvolutionInvariant s' (k + 1)

evolution_step s s' k inv_k trans h_no_error =
  record
    { h_step_eq = StepTransition.step_increments trans
    ; h_error = h_no_error
    ; h_state_valid = ?  -- state remains valid-dimensioned after step
    ; h_ham_valid = EvolutionInvariant.h_ham_valid inv_k
    ; h_dt_pos = EvolutionInvariant.h_dt_pos inv_k
    ; h_in_range = ?  -- (k+1) ≀ num_steps follows from k ≀ num_steps and loop guard
    ; h_accumulated_time = StepTransition.time_advances trans
    ; h_norm_schedule = Ξ» m h_lt h_mod β†’
        let h_le = <-to-≀ h_lt
        in case (decide (m ≑ k + 1)) of Ξ» where
             (yes p) β†’
               -- m = k+1, check if normalization_log updated
               if (k + 1) mod 100 ≑ 0 then true else ?
             (no Β¬p) β†’
               -- m < k+1 and m β‰  k+1, so m ≀ k, use old log
               EvolutionInvariant.h_norm_schedule inv_k m (≀-to-< h_le Β¬p) h_mod
    }

-- ============================================================================
-- Exit Condition: Loop termination at k = num_steps
-- ============================================================================

-- When loop exits (k ≑ num_steps), postcondition is satisfied
evolution_exit :
  (s : EvolutionState) (k : β„•) β†’
  EvolutionInvariant s k β†’
  k ≑ EvolutionState.num_steps s β†’
  -- Then:
  -- 1. Loop has completed all iterations
  (loopCompleted k (EvolutionState.num_steps s)) ∧
  -- 2. Error status is success
  (errorIsClear (EvolutionState.error_status s)) ∧
  -- 3. State is valid (ready for measurement/output)
  (isValidDim (EvolutionState.state s)) ∧
  -- 4. Total time accumulated matches intended duration
  (EvolutionState.accumulated_time s ≑
   (ℝ.fromβ„• k) * (EvolutionState.dt s))

evolution_exit s k inv_k h_done =
  ⟨ h_done
  , EvolutionInvariant.h_error inv_k
  , EvolutionInvariant.h_state_valid inv_k
  , EvolutionInvariant.h_accumulated_time inv_k
  ⟩