From fc10b363b3c35313ac2f1bf14f83daec2bf22c41 Mon Sep 17 00:00:00 2001
From: Thomas Albers Raviola <thomas@thomaslabs.org>
Date: Tue, 4 Jun 2024 11:26:32 +0200
Subject: Throw exception on linear dependence

---
 solvers.py           |  4 ++--
 test/test_solvers.py | 12 +++++-------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/solvers.py b/solvers.py
index 72f1b1d..38ac247 100644
--- a/solvers.py
+++ b/solvers.py
@@ -92,7 +92,7 @@ def gaussian_eliminate(
         aa: NDArray[np.float_],
         bb: NDArray[np.float_],
         tolerance: float = 1e-6
-) -> NDArray[np.float_] | None:
+) -> NDArray[np.float_]:
     '''Solves a linear system of equations (A x = b) by LUP factorization.
 
     Args:
@@ -108,7 +108,7 @@ def gaussian_eliminate(
     nn = uu.shape[0]
     # Check if rank of matrix is lower than nn
     if np.abs(uu[nn - 1, nn - 1]) < tolerance:
-        return None
+        raise ValueError
 
     # L y = P @ b
     y = forward_substitution(ll, pp @ bb)
diff --git a/test/test_solvers.py b/test/test_solvers.py
index a7c175f..b049cca 100644
--- a/test/test_solvers.py
+++ b/test/test_solvers.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 """Contains routines to test the solvers module"""
 
+import pytest
 import numpy as np
 from numpy.typing import NDArray
 
@@ -27,11 +28,10 @@ def test_pivot_3() -> None:
 
 def test_lindep_3() -> None:
     """Tests a linearly dependent system wit three variables."""
-    aa = np.array([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [7.0, 8.0, 9.0]])
-    bb = np.array([1.0, 2.0, 3.0])
-    xx_expected = None
-    xx_gauss = solvers.gaussian_eliminate(aa, bb)
-    assert xx_expected == xx_gauss
+    with pytest.raises(ValueError):
+        aa = np.array([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [7.0, 8.0, 9.0]])
+        bb = np.array([1.0, 2.0, 3.0])
+        xx_gauss = solvers.gaussian_eliminate(aa, bb)
 
 
 def test_lu_factorization() -> None:
@@ -45,7 +45,6 @@ def test_forward_substitution() -> None:
     bb = np.array([3.0, 2.0, 1.0])
     xx_result = solvers.forward_substitution(ll, bb)
     xx_expected = np.array([3 / 2, 7.0 / 4.0, -6])
-    print(xx_result)
     assert np.allclose(xx_expected, xx_result)
 
 def test_back_substitution() -> None:
@@ -53,5 +52,4 @@ def test_back_substitution() -> None:
     bb = np.array([1.0, 2.0, 3.0])
     xx_result = solvers.back_substitution(uu, bb)
     xx_expected = np.array([-6, 7.0 / 4.0, 3.0 / 2.0])
-    print(xx_result)
     assert np.allclose(xx_expected, xx_result)
-- 
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