ldpc_optical/model/test_density_evolution.py

#!/usr/bin/env python3
"""Tests for density evolution optimizer."""

import numpy as np
import pytest
import sys
import os

sys.path.insert(0, os.path.dirname(__file__))


class TestDensityEvolution:
    """Tests for the Monte Carlo DE engine."""

    def test_de_known_good_converges(self):
        """DE with original staircase profile at lam_s=10 should converge easily."""
        from density_evolution import run_de, ORIGINAL_STAIRCASE_PROFILE
        np.random.seed(42)
        converged, error_frac = run_de(
            ORIGINAL_STAIRCASE_PROFILE, lam_s=10.0, lam_b=0.1,
            z_pop=10000, max_iter=50
        )
        assert converged, f"DE should converge at lam_s=10, error_frac={error_frac}"

    def test_de_known_bad_fails(self):
        """DE at very low lam_s=0.1 should not converge."""
        from density_evolution import run_de, ORIGINAL_STAIRCASE_PROFILE
        np.random.seed(42)
        converged, error_frac = run_de(
            ORIGINAL_STAIRCASE_PROFILE, lam_s=0.1, lam_b=0.1,
            z_pop=10000, max_iter=50
        )
        assert not converged, f"DE should NOT converge at lam_s=0.1, error_frac={error_frac}"

    def test_de_population_shape(self):
        """Verify belief arrays have correct shapes after one step."""
        from density_evolution import de_channel_init, density_evolution_step
        np.random.seed(42)
        n_base = 8
        m_base = 7
        z_pop = 1000

        # Original staircase H_base profile
        from density_evolution import ORIGINAL_STAIRCASE_PROFILE
        beliefs, msg_memory = de_channel_init(ORIGINAL_STAIRCASE_PROFILE, z_pop, lam_s=5.0, lam_b=0.1)

        # beliefs should be (n_base, z_pop)
        assert beliefs.shape == (n_base, z_pop), f"Expected ({n_base}, {z_pop}), got {beliefs.shape}"

        # Run one step
        beliefs = density_evolution_step(beliefs, msg_memory, ORIGINAL_STAIRCASE_PROFILE, z_pop)
        assert beliefs.shape == (n_base, z_pop), f"Shape changed after step: {beliefs.shape}"


class TestThresholdComputation:
    """Tests for threshold binary search."""

    def test_threshold_original_staircase(self):
        """Threshold for original staircase [7,2,2,2,2,2,2,1] should be ~3-6 photons."""
        from density_evolution import compute_threshold_for_profile
        np.random.seed(42)
        threshold = compute_threshold_for_profile(
            [7, 2, 2, 2, 2, 2, 2, 1], m_base=7, lam_b=0.1,
            z_pop=10000, tol=0.5
        )
        assert 2.0 < threshold < 8.0, f"Expected threshold ~3-6, got {threshold}"

    def test_threshold_peg_ring(self):
        """PEG ring [7,3,3,3,2,2,2,2] should have lower or equal threshold than original."""
        from density_evolution import compute_threshold_for_profile
        np.random.seed(42)
        thresh_orig = compute_threshold_for_profile(
            [7, 2, 2, 2, 2, 2, 2, 1], m_base=7, lam_b=0.1,
            z_pop=15000, tol=0.25
        )
        np.random.seed(123)
        thresh_peg = compute_threshold_for_profile(
            [7, 3, 3, 3, 2, 2, 2, 2], m_base=7, lam_b=0.1,
            z_pop=15000, tol=0.25
        )
        assert thresh_peg <= thresh_orig, (
            f"PEG threshold {thresh_peg} should be <= original {thresh_orig}"
        )

    def test_profile_to_hbase(self):
        """build_de_profile should produce valid profile with correct column degrees."""
        from density_evolution import build_de_profile
        profile = build_de_profile([7, 3, 2, 2, 2, 2, 2, 2], m_base=7)
        assert profile['n_base'] == 8
        assert profile['m_base'] == 7
        assert profile['vn_degrees'] == [7, 3, 2, 2, 2, 2, 2, 2]
        # Every row should have at least 2 connections
        for r, conns in enumerate(profile['connections']):
            assert len(conns) >= 2, f"Row {r} has only {len(conns)} connections"


class TestDegreeDistributionOptimizer:
    """Tests for the exhaustive search optimizer."""

    def test_enumerate_candidates(self):
        """Enumeration should produce 3^7 = 2187 candidates."""
        from density_evolution import enumerate_vn_candidates
        candidates = enumerate_vn_candidates(m_base=7)
        assert len(candidates) == 3**7, f"Expected 2187, got {len(candidates)}"
        # Each candidate should have 8 elements (info col + 7 parity)
        for c in candidates:
            assert len(c) == 8
            assert c[0] == 7  # info column always degree 7

    def test_filter_removes_invalid(self):
        """Filter should keep valid distributions and remove truly invalid ones."""
        from density_evolution import filter_by_row_degree
        # All-dv=2 parity: parity_edges=14, dc_avg=3 -> valid for [3,6]
        all_2 = [7, 2, 2, 2, 2, 2, 2, 2]
        assert filter_by_row_degree([all_2], m_base=7, dc_min=3, dc_max=6) == [all_2]
        # All-dv=4 parity: parity_edges=28, dc_avg=5 -> valid for [3,6]
        all_4 = [7, 4, 4, 4, 4, 4, 4, 4]
        assert filter_by_row_degree([all_4], m_base=7, dc_min=3, dc_max=6) == [all_4]
        # A hypothetical all-dv=1 parity: parity_edges=7, total=14, avg dc=2 < 3 -> invalid
        all_1 = [7, 1, 1, 1, 1, 1, 1, 1]
        assert filter_by_row_degree([all_1], m_base=7, dc_min=3, dc_max=6) == []
        # With tighter constraints (dc_min=4), all-dv=2 should be removed
        assert filter_by_row_degree([all_2], m_base=7, dc_min=4, dc_max=6) == []

    def test_optimizer_finds_better_than_original(self):
        """Optimizer should find a distribution with threshold <= original staircase."""
        from density_evolution import optimize_degree_distribution, compute_threshold_for_profile
        np.random.seed(42)
        results = optimize_degree_distribution(m_base=7, lam_b=0.1, top_k=5, z_pop_coarse=5000, z_pop_fine=10000, tol=0.5)
        assert len(results) > 0, "Optimizer should return at least one result"
        best_degrees, best_threshold = results[0]
        # Original staircase threshold is ~3-5 photons
        assert best_threshold < 6.0, f"Best threshold {best_threshold} should be < 6.0"


class TestPEGBaseMatrixConstructor:
    """Tests for the PEG base matrix constructor."""

    def test_construct_matches_target_degrees(self):
        """Constructed matrix should have the target column degrees."""
        from density_evolution import construct_base_matrix
        np.random.seed(42)
        target = [7, 3, 3, 3, 2, 2, 2, 2]
        H_base, girth = construct_base_matrix(target, z=32, n_trials=500)
        # Check column degrees
        for c in range(H_base.shape[1]):
            actual_deg = np.sum(H_base[:, c] >= 0)
            assert actual_deg == target[c], (
                f"Col {c}: expected degree {target[c]}, got {actual_deg}"
            )

    def test_construct_has_valid_rank(self):
        """Full H matrix should have full rank, parity submatrix should too."""
        from density_evolution import construct_base_matrix, verify_matrix
        np.random.seed(42)
        target = [7, 3, 3, 3, 2, 2, 2, 2]
        H_base, girth = construct_base_matrix(target, z=32, n_trials=500)
        checks = verify_matrix(H_base, z=32)
        assert checks['full_rank'], f"Full matrix rank {checks['actual_rank']} < expected {checks['expected_rank']}"
        assert checks['parity_rank'], f"Parity submatrix not full rank"

    def test_construct_encodable(self):
        """Encoding a random info word should produce zero syndrome."""
        from density_evolution import construct_base_matrix, verify_matrix
        np.random.seed(42)
        target = [7, 3, 3, 3, 2, 2, 2, 2]
        H_base, girth = construct_base_matrix(target, z=32, n_trials=500)
        checks = verify_matrix(H_base, z=32)
        assert checks['encodable'], "Should be able to encode and verify syndrome=0"

    def test_construct_girth_at_least_4(self):
        """Constructed matrix should have girth >= 4."""
        from density_evolution import construct_base_matrix
        np.random.seed(42)
        target = [7, 3, 3, 3, 2, 2, 2, 2]
        H_base, girth = construct_base_matrix(target, z=32, n_trials=500)
        assert girth >= 4, f"Girth {girth} should be >= 4"


class TestFERValidationAndCLI:
    """Tests for FER validation and CLI."""

    def test_validate_returns_results(self):
        """validate_matrix should return FER results dict."""
        from density_evolution import validate_matrix
        from ldpc_sim import H_BASE
        np.random.seed(42)
        results = validate_matrix(H_BASE, lam_s_points=[10.0], n_frames=10, lam_b=0.1)
        assert 10.0 in results, f"Expected key 10.0, got {list(results.keys())}"
        assert 'fer' in results[10.0]
        assert 0.0 <= results[10.0]['fer'] <= 1.0

    def test_cli_threshold(self):
        """CLI threshold subcommand should exit 0."""
        import subprocess
        result = subprocess.run(
            ['python3', 'model/density_evolution.py', 'threshold', '--z-pop', '5000', '--tol', '1.0'],
            capture_output=True, text=True, timeout=120,
        )
        assert result.returncode == 0, f"CLI failed: {result.stderr}"
        assert 'threshold' in result.stdout.lower() or 'photon' in result.stdout.lower()


class TestNormalizedMinSum:
    """Tests for normalized min-sum CN update mode."""

    def test_normalized_minsun_output_smaller(self):
        """Normalized min-sum should scale magnitude by alpha, not subtract offset."""
        from ldpc_sim import min_sum_cn_update
        # Input: [10, -15, 20] -> min1=10 (idx0), min2=15
        # Offset mode: output magnitudes = max(0, mag - 1)
        #   idx0 gets min2=15, so mag=14; idx1,2 get min1=10, so mag=9
        # Normalized mode (alpha=0.75): output magnitudes = floor(mag * 0.75)
        #   idx0 gets min2=15, so mag=floor(15*0.75)=11; idx1,2 get min1=10, so mag=floor(10*0.75)=7
        result_norm = min_sum_cn_update([10, -15, 20], cn_mode='normalized', alpha=0.75)
        # idx0: min2=15, floor(15*0.75)=11, sign=XOR(1,0)^0=1^0=1 -> negative? No.
        # signs = [0, 1, 0], sign_xor = 1
        # idx0: ext_sign = 1^0 = 1 -> -11
        # idx1: ext_sign = 1^1 = 0, mag=floor(10*0.75)=7 -> 7
        # idx2: ext_sign = 1^0 = 1, mag=floor(10*0.75)=7 -> -7
        assert result_norm[0] == -11, f"Expected -11, got {result_norm[0]}"
        assert result_norm[1] == 7, f"Expected 7, got {result_norm[1]}"
        assert result_norm[2] == -7, f"Expected -7, got {result_norm[2]}"

    def test_normalized_decode_converges(self):
        """Decode a known codeword at lam_s=5 with normalized min-sum."""
        from ldpc_analysis import generic_decode, peg_encode, build_peg_matrix
        from ldpc_sim import poisson_channel, quantize_llr
        np.random.seed(42)
        H_base, H_full = build_peg_matrix(z=32)
        k = 32
        info = np.zeros(k, dtype=np.int8)
        codeword = peg_encode(info, H_base, H_full, z=32)
        llr_float, _ = poisson_channel(codeword, lam_s=5.0, lam_b=0.1)
        llr_q = quantize_llr(llr_float)
        decoded, converged, iters, sw = generic_decode(
            llr_q, H_base, z=32, max_iter=30, cn_mode='normalized', alpha=0.75
        )
        assert converged, f"Normalized min-sum should converge at lam_s=5, sw={sw}"
        assert np.all(decoded == info), f"Decoded bits don't match"

    def test_offset_mode_unchanged(self):
        """Default offset mode should produce identical results to before."""
        from ldpc_sim import min_sum_cn_update
        # Test with explicit cn_mode='offset' and without (default)
        msgs = [10, -15, 20, -5]
        result_default = min_sum_cn_update(msgs)
        result_explicit = min_sum_cn_update(msgs, cn_mode='offset')
        assert result_default == result_explicit, (
            f"Default and explicit offset should match: {result_default} vs {result_explicit}"
        )