raise ValueError if the the number of regression points is less than the number of parameters in _residual

news/enough-regression-points.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* Raise ``ValueError`` if the number of shared grid points between morphed and target functions is less than the number of parameters.
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

src/diffpy/morph/refine.py

@@ -83,7 +83,15 @@ def _residual(self, pvals):
  self.x_morph, self.y_morph, self.x_target, self.y_target
  )
  rvec = _y_target - _y_morph
-
+ if len(rvec) < len(pvals):
+ raise ValueError(
+ f"\nNumber of parameters (currently {len(pvals)}) cannot "
+ "exceed the number of shared grid points "
+ f"(currently {len(rvec)}). "
+ "Please reduce the number of morphing parameters or "
+ "provide new morphing and target functions with more "
+ "shared grid points."
+ )
  # If first time computing residual
  if self.res_length is None:
  self.res_length = len(rvec)
@@ -145,6 +153,9 @@ def refine(self, *args, **kw):
  ------
  ValueError
  Exception raised if a minimum cannot be found.
+ ValueError
+ If the number of shared grid points between morphed function and
+ target function is smaller than the number of parameters.
  """
 
  self.pars = args or self.chain.config.keys()

tests/test_refine.py

@@ -181,6 +181,62 @@ def stretch(x, y, stretch):
 
  assert res < err
 
+ def test_refine_grid_bad(self, user_filesystem):
+ grid = numpy.arange(2)
+ func = numpy.sin(grid)
+ grid1, func1, grid2, func2 = grid, func, grid, func
+ config = {
+ "stretch": 0.005,
+ "scale": 1.0,
+ "smear": 0,
+ }
+ chain = MorphChain(config)
+ refiner = Refiner(chain, grid1, func1, grid2, func2)
+ refpars = ["stretch", "scale", "smear"]
+ expected_error_message = (
+ "\nNumber of parameters (currently 3) cannot "
+ "exceed the number of shared grid points "
+ "(currently 2). "
+ "Please reduce the number of morphing parameters or "
+ "provide new morphing and target functions with more "
+ "shared grid points."
+ )
+ with pytest.raises(
+ ValueError,
+ ) as error:
+ refiner.refine(*refpars)
+ actual_error_message = str(error.value)
+ assert actual_error_message == expected_error_message
+
+ # call from command line
+ import subprocess
+
+ data_dir_path = user_filesystem / "cwd_dir"
+ morph_file = data_dir_path / "morph_data"
+ morph_data_text = [
+ str(grid1[i]) + " " + str(func1[i]) for i in range(len(grid1))
+ ]
+ morph_data_text = "\n".join(morph_data_text)
+ morph_file.write_text(morph_data_text)
+ target_file = data_dir_path / "target_data"
+ target_data_text = [
+ str(grid2[i]) + " " + str(func2[i]) for i in range(len(grid2))
+ ]
+ target_data_text = "\n".join(target_data_text)
+ target_file.write_text(target_data_text)
+ run_cmd = ["diffpy.morph"]
+ for key, value in config.items():
+ run_cmd.append(f"--{key}")
+ run_cmd.append(f"{value}")
+ run_cmd.extend([str(morph_file), str(target_file)])
+ run_cmd.append("-n")
+ result = subprocess.run(run_cmd, capture_output=True, text=True)
+ expected_error_message = (
+ "diffpy.morph: error: " + expected_error_message
+ )
+ actual_error_message = result.stderr.strip()
+ assert actual_error_message == expected_error_message
+
 
 # End of class TestRefine