# 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:
```cpp
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.