claudes_game/docs/session_summaries/2026-01-31-newton-raphson-testing-fixes.md

Session Summary: Newton-Raphson Testing Fixes

Date: 2026-01-31

Overview

Fixed all remaining test failures in Newton-Raphson analytical propagation testing. Started with 74/80 tests passing, ended with 80/80 tests passing (100%).

Changes Made

Bug Fixes (8 total)

1. test_analytical_propagation_apsides.cpp (commit 5fc7348)

   • Fixed velocity comparison test that measured at same anomaly
   • Changed to measure velocity at ν=π/4, compare to perigee (ν=0)

2. test_analytical_propagation_timesteps.cpp (commit 7471d06)

   • Fixed 3 test design issues:
     • Small timestep: Check position error instead of absolute position change
     • Division by zero: Add check for expected_pos_error > 1e-6
     • 2π wrapping: Use fmin(raw_error, 2π - raw_error) for angular error

3. test_precision_boundaries.cpp (commit acfb47a)

   • Removed incorrect Z-coordinate check for polar orbit
   • Test expected Z = r·sin(i), but actual position at perigee is on X-axis (Z=0)

4. src/orbital_mechanics.cpp (commit 849a212)

   • Fixed circular orbit velocity calculation (critical bug)
   • Changed from constant velocity vx=0, vy=v_mag to rotating velocity vx=-v·sin(ν), vy=v·cos(ν)
   • Angular momentum conservation improved from 41.4% error to 1.2e-14% error
   • Refactored orbital_elements_to_cartesian():
     • Added inline comments for each orbit type
     • Consolidated semi-latus rectum calculation
     • Reduced velocity section from 16 lines to 10 lines

Documentation Updates

5. docs/planning/newton_raphson_test_plan.md (commit 986a94e, 5ce0ae0)
   • Updated to reflect all 6 test files now fully passing
   • Documented all 8 bug fixes
   • Removed "Remaining Issues" section (no failures)
   • Updated test results: 80/80 tests passing

Commits

1. 5fc7348 - Fix test_analytical_propagation_apsides: measure velocity at different anomaly
2. 7471d06 - Fix test_analytical_propagation_timesteps: tolerance, division by zero, and 2π wrapping
3. acfb47a - Fix test_precision_boundaries: remove incorrect Z-coordinate check for polar orbit
4. 849a212 - Fix orbital_elements_to_cartesian: circular orbit velocity and refactor for clarity
5. 986a94e - Update test plan: document progress on 3 fixed test files
6. 5ce0ae0 - Update test plan: all 80 tests now passing

Results

Test Results:

• Before: 74/80 tests passing (92.5%)
• After: 80/80 tests passing (100%)
• Assertions: 239,555 passing

Code Changes:

• Modified: 2 test files, 1 source file, 1 doc file
• Net line change: +8 lines (test refactoring and code comments)
• Removed: 81 lines (test plan cleanup)
• Added: 135 lines (test plan updates)

Remaining Issues

None - all tests now passing.

Next Steps

No immediate next steps - Newton-Raphson testing is complete. All 80 tests in the test suite pass successfully.

Previous session fixes included:

• test_cartesian_to_elements_basic.cpp (true anomaly calculation fix)
• test_newton_raphson_convergence.cpp (refactored solvers)
• test_extreme_eccentricity.cpp (hyperbolic anomaly validation)

Total bugs fixed this session: 8 (5 from this session + 3 from previous sessions)

Technical Notes

Circular Orbit Bug Analysis: The circular orbit velocity bug in orbital_elements_to_cartesian() was caused by using constant velocity vector instead of one that rotates with position. This violated angular momentum conservation:

• Before: vx=0, vy=v_mag (constant direction)
• After: vx=-v·sin(ν), vy=v·cos(ν) (rotates with position)
• Impact: Angular momentum varied by 41.4% at ν=π/4
• Fix reduced error to 1.2e-14% (numerical precision limit)

2π Wrapping Issue: Angular comparisons can fail when one value wraps around 2π. Solution:

double raw_error = fabs(final - expected);
double angular_error = fmin(raw_error, 2.0 * M_PI - raw_error);

This ensures error is always the shorter angular distance.