enh: introduce UnsupportedModelParametersError to detect bad model pa…

…ramters for the rytov-sc model

CHANGELOG

@@ -1,3 +1,6 @@
+0.5.4
+ - enh: introduce UnsupportedModelParametersError to detect bad model
+   paramters for the rytov-sc model
 0.5.3
  - fix: also guess initial values for image method if edge detection
    is ill-defined (RadiusExceedsImageSizeError)

qpsphere/models/excpt.py

@@ -0,0 +1,3 @@
+class UnsupportedModelParametersError(BaseException):
+    """Used when a specific model cannot handle input parameters"""
+    pass

qpsphere/models/mod_rytov_sc.py

@@ -1,6 +1,11 @@
 import numpy as np
 
 from . import mod_rytov
+from .excpt import UnsupportedModelParametersError
+
+
+class RefractiveIndexLowerThanMediumError(UnsupportedModelParametersError):
+    pass
 
 
 #: correction parameters (see :func:`correct_rytov_output`)
@@ -43,6 +48,11 @@ def correct_rytov_sc_input(radius_sc, sphere_index_sc, medium_index,
     """
     params = get_params(radius_sampling)
 
+    if sphere_index_sc < medium_index:
+        raise RefractiveIndexLowerThanMediumError(
+            "The object refractive index {} is ".format(sphere_index_sc)
+            + "lower than that of the medium {} ".format(medium_index)
+            + "which is not supported by the rytov-sc model.")
     # sage script:
     # var('sphere_index, sphere_index_sc, na, nb, medium_index')
     # x = sphere_index / medium_index - 1

tests/test_rytov_sc.py

@@ -1,6 +1,6 @@
 import numpy as np
 
-from qpsphere.models import mod_rytov_sc, mod_rytov
+from qpsphere.models import excpt, mod_rytov_sc, mod_rytov
 
 
 def test_parameter_inversion():
@@ -46,6 +46,22 @@ def test_basic():
     assert np.all(qpi.pha == qpi_sc.pha)
 
 
+def test_unsupported_parameters():
+    kwargs = dict(grid_size=(20, 20),
+                  center=(9.5, 9.5),
+                  radius=5e-6,
+                  sphere_index=1.330,
+                  medium_index=1.333,
+                  wavelength=550e-9,
+                  pixel_size=1e-6)
+    try:
+        mod_rytov_sc.rytov_sc(**kwargs)
+    except excpt.UnsupportedModelParametersError:
+        pass
+    else:
+        assert False, "Sphere index lower than medium should error out"
+
+
 if __name__ == "__main__":
     # Run all tests
     loc = locals()