fix(ops): Fix ops.argmin() handling of subnormal float values in Kera…

…s backends (#20812)

- Update JAX and NumPy backends to handle subnormal float comparisons

- Add test case to verify subnormal float value handling

keras/src/backend/jax/numpy.py

@@ -364,7 +364,20 @@ def argmax(x, axis=None, keepdims=False):
 
 
 def argmin(x, axis=None, keepdims=False):
-    return jnp.argmin(x, axis=axis, keepdims=keepdims)
+    x_64 = jnp.asarray(x, dtype=jnp.float64)
+    if axis is not None:
+        min_mask = x_64 == jnp.min(x_64, axis=axis, keepdims=True)
+        indices = jnp.argmin(
+            jnp.where(min_mask, x_64, jnp.inf), axis=axis, keepdims=keepdims
+        ).astype("int32")
+    else:
+        min_mask = (x_64 < x_64.min()) | (
+            (x_64 == x_64.min()) & (jnp.signbit(x_64))
+        )
+        indices = jnp.argmin(
+            jnp.where(min_mask, x_64, jnp.inf), axis=axis, keepdims=keepdims
+        ).astype("int32")
+    return indices
 
 
 def argsort(x, axis=-1):

keras/src/backend/numpy/numpy.py

@@ -257,7 +257,20 @@ def argmax(x, axis=None, keepdims=False):
 
 def argmin(x, axis=None, keepdims=False):
     axis = standardize_axis_for_numpy(axis)
-    return np.argmin(x, axis=axis, keepdims=keepdims).astype("int32")
+    x_64 = np.asarray(x, dtype=np.float64)
+    if axis is not None:
+        min_mask = x_64 == np.min(x_64, axis=axis, keepdims=True)
+        indices = np.argmin(
+            np.where(min_mask, x_64, np.inf), axis=axis, keepdims=keepdims
+        ).astype("int32")
+    else:
+        min_mask = (x_64 < x_64.min()) | (
+            (x_64 == x_64.min()) & (np.signbit(x_64))
+        )
+        indices = np.argmin(
+            np.where(min_mask, x_64, np.inf), axis=axis, keepdims=keepdims
+        ).astype("int32")
+    return indices
 
 
 def argsort(x, axis=-1):

keras/src/ops/numpy_test.py

@@ -1152,6 +1152,28 @@ def test_argmax_negative_zero(self):
         )
         self.assertEqual(knp.argmax(input_data), 2)
 
+    @pytest.mark.skipif(
+        keras.config.backend() == "openvino"
+        or keras.config.backend() == "tensorflow",
+        reason="""
+        OpenVINO and TensorFlow don't support this 
+        change, TensorFlow behavior for this case is under
+        evaluation and may change within this PR
+        """,
+    )
+    def test_argmin_negative_zero(self):
+        input_data = np.array(
+            [
+                0.0,
+                1.1754943508222875e-38,
+                -1.401298464324817e-45,
+                0.0,
+                459367.0,
+            ],
+            dtype=np.float32,
+        )
+        self.assertEqual(knp.argmin(input_data), 2)
+
     def test_argmin(self):
         x = KerasTensor((None, 3))
         self.assertEqual(knp.argmin(x).shape, ())