[ENH] Add Greenstone example model and CG solver tests (#1048)

# Description
Added a new Greenstone example model to GemPy with supporting functionality. The implementation includes:

- Added a new `GREENSTONE` enum to `ExampleModel`
- Created a `_generate_greenstone_model` function in the examples generator
- Added the binary Greenstone.gempy model file
- Updated the interpolation input factory to handle weights from solutions
- Added tests for the Greenstone model including CG solver tests with PyKeops

Relates to #weights-caching-and-cg-solver

# Checklist
- [x] My code uses type hinting for function and method arguments and return values.
- [x] I have created tests which cover my code.
- [x] The test code either 1. demonstrates at least one valuable use case (e.g. integration tests) 
or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
- [x] New tests pass locally with my changes.

Author: Leguark

examples/data/gempy_models/Greenstone.gempy

@@ -215,20 +215,15 @@
 # %%
 # Setting verbose and condition number options for debugging
 geo_model.interpolation_options.kernel_options.compute_condition_number = True
-# %%
-# Observations and parameter adjustments
-# The octree refinement is making the octree grid almost dense, and smaller chunks are needed to avoid running out of memory.
-# Adjusting parameters accordingly:
-
-geo_model.interpolation_options.evaluation_options.evaluation_chunk_size = 50_000
 
 # %% 
 gp.compute_model(
     gempy_model=geo_model,
     engine_config=gp.data.GemPyEngineConfig(
         backend=gp.data.AvailableBackends.PYTORCH,
         dtype='float64'
-    )
+    ),
+    validate_serialization=False
 )
 
 # %% 

examples/examples/real/Hecho.py

@@ -4,7 +4,6 @@
 from typing import Optional
 
 import gempy_engine
-from gempy.API.gp2_gp3_compatibility.gp3_to_gp2_input import gempy3_to_gempy2
 from gempy_engine.config import AvailableBackends
 from gempy_engine.core.backend_tensor import BackendTensor
 from gempy_engine.core.data import Solutions
@@ -14,7 +13,6 @@
 from ..core.data.geo_model import GeoModel
 from ..modules.data_manipulation import interpolation_input_from_structural_frame
 from ..modules.optimize_nuggets import nugget_optimizer
-from ..optional_dependencies import require_gempy_legacy
 
 dotenv.load_dotenv()
 

gempy/API/compute_API.py

@@ -25,6 +25,8 @@ def generate_example_model(example_model: ExampleModel, compute_model: bool = Tr
             return _generate_one_fault_model_gravity(compute_model)
         case ExampleModel.GRABEN:
             return _generate_graben_model(compute_model)
+        case ExampleModel.GREENSTONE:
+            return _generate_greenstone_model(compute_model)
         case _:
             raise NotImplementedError(f"Example model {example_model} not implemented.")
 
@@ -482,3 +484,26 @@ def _generate_graben_model(compute_model: bool) -> gp.data.GeoModel:
 
     return geo_data
 
+
+def _generate_greenstone_model(compute_model: bool) -> gp.data.GeoModel:
+    test_dir = os.path.dirname(os.path.abspath(__file__))
+
+    # Build the path relative to the test file location
+    path = os.path.join(test_dir, '..', '..', 'examples', 'data', 'gempy_models', 'Greenstone.gempy')
+    with open(path, 'rb') as f:
+        binary_file = f.read()
+
+    from gempy.modules.serialization.save_load import _load_model_from_bytes
+    geo_model: gp.data.GeoModel = _load_model_from_bytes(binary_file)
+    
+    if compute_model:
+        sol = gp.compute_model(
+            gempy_model=geo_model,
+            engine_config=gp.data.GemPyEngineConfig(
+                backend=gp.data.AvailableBackends.numpy,
+                dtype='float32'
+            )
+    )
+    return geo_model
+        
+

gempy/API/examples_generator.py

@@ -9,3 +9,4 @@ class ExampleModel(Enum):
     COMBINATION = auto()
     ONE_FAULT_GRAVITY = auto()
     GRABEN = auto()
+    GREENSTONE = auto()

gempy/core/data/enumerators.py

@@ -42,11 +42,18 @@ def interpolation_input_from_structural_frame(geo_model: "gempy.data.GeoModel")
         extent_transformed=geo_model.extent_transformed_transformed_by_input
     )
 
+    weights = []
+    if geo_model.solutions is not None:
+        for stack_sol in geo_model.solutions.root_output.outputs_centers:
+            weights.append(stack_sol.weights)
+    
+
     interpolation_input: InterpolationInput = InterpolationInput(
         surface_points=surface_points,
         orientations=orientations,
         grid=grid,
-        unit_values=structural_frame.elements_ids  # TODO: Here we will need to pass densities etc.
+        unit_values=structural_frame.elements_ids,  # TODO: Here we will need to pass densities etc.
+        weights=weights
     )
 
     return interpolation_input

gempy/modules/data_manipulation/_engine_factory.py

@@ -25,6 +25,7 @@ def nugget_optimizer(
         engine_backend=engine_cfg.backend,
         use_gpu=engine_cfg.use_gpu,
         dtype=engine_cfg.dtype,
+        grads=True
     )
 
     # 2) Prepare data

gempy/modules/optimize_nuggets/_optimizer.py

@@ -1,5 +1,5 @@
 -r requirements.txt
 
 # This install matplotlib
-gempy_viewer~=2025.1.0
+gempy_viewer~=2025.1.4
 pandas

requirements/base-requirements.txt

@@ -1,2 +1,2 @@
 # This install also numpy
-gempy_engine>=2025.2.0dev0,<2025.3.0
+gempy_engine>=2025.3.0dev0,<2025.4.0

requirements/requirements.txt

@@ -80,4 +80,13 @@ def test_generate_combination_model():
         model=model,
         name="Combination Scalar Field"
     )
-    
+
+
+def test_generate_greenstone_model():
+    model = gp.generate_example_model(ExampleModel.GREENSTONE, compute_model=True)
+    print(model.structural_frame)
+
+    if PLOT:
+        gpv = require_gempy_viewer()
+        gpv.plot_3d(model, image=True)
+