add tests

src/mrpro/operators/Jacobian.py

@@ -1,6 +1,7 @@
 """Jacobian."""
 
 from collections.abc import Callable
+from typing import Unpack
 
 import torch
 
@@ -25,7 +26,7 @@ def __init__(self, operator: Operator[torch.Tensor, tuple[torch.Tensor]], *x0: t
             point at which to linearize the operator
         """
         super().__init__()
-        self._vjp: Callable[tuple[torch.Tensor, ...], tuple[torch.Tensor, ...]] | None = None
+        self._vjp: Callable[[Unpack[tuple[torch.Tensor, ...]]], tuple[torch.Tensor, ...]] | None = None
         self._x0: tuple[torch.Tensor, ...] = x0
         self._operator = operator
         self._f_x0: tuple[torch.Tensor, ...] | None = None

tests/operators/test_jacobian.py

@@ -7,6 +7,7 @@
 
 
 def test_jacobian_adjointness():
+    """Test adjointness of Jacobian operator."""
     rng = RandomGenerator(123)
     x = rng.float32_tensor(3)
     y = rng.float32_tensor(())
@@ -17,10 +18,34 @@ def test_jacobian_adjointness():
 
 
 def test_jacobian_taylor():
+    """Test Taylor expansion"""
     rng = RandomGenerator(123)
     x0 = rng.float32_tensor(3)
     x = x0 + 1e-2 * rng.float32_tensor(3)
     op = L2NormSquared()
     jacobian = Jacobian(op, x0)
     fx = jacobian.taylor(x)
     torch.testing.assert_close(fx, op(x), rtol=1e-3, atol=1e-3)
+
+
+def test_jacobian_gaussnewton():
+    """Test Gauss Newton approximation of the Hessian"""
+    rng = RandomGenerator(123)
+    x0 = rng.float32_tensor(3)
+    x = x0 + 1e-2 * rng.float32_tensor(3)
+    op = L2NormSquared()
+    jacobian = Jacobian(op, x0)
+    (actual,) = jacobian.gauss_newton(x)
+    expected = torch.vdot(x, x0) * 4 * x0  # analytical solution for L2NormSquared
+    torch.testing.assert_close(actual, expected, rtol=1e-3, atol=1e-3)
+
+
+def test_jacobian_valueatx0():
+    """Test value at x0"""
+    rng = RandomGenerator(123)
+    x0 = rng.float32_tensor(3)
+    op = L2NormSquared()
+    jacobian = Jacobian(op, x0)
+    (actual,) = jacobian.value_at_x0
+    (expected,) = op(x0)
+    torch.testing.assert_close(actual, expected, rtol=1e-3, atol=1e-3)