Add spline chi-squared calculation.

lsst · Apr 19, 2024 · d7494a3 · d7494a3
1 parent 41d53da
commit d7494a3
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Showing 3 changed files with 31 additions and 1 deletion.
diff --git a/python/lsst/cp/pipe/linearity.py b/python/lsst/cp/pipe/linearity.py
@@ -577,6 +577,8 @@ def run(self, inputPtc, dummy, camera, inputDims,
                                        "be consistent with zero.")
                 pars[0] = 0.0
 
+                linearityChisq = fitter.compute_chisq_dof(pars)
+
                 linearityCoeffs = np.concatenate([nodes, pars[fitter.par_indices["values"]]])
                 linearFit = np.array([0.0, np.mean(pars[fitter.par_indices["groups"]])])
 
@@ -608,7 +610,7 @@ def run(self, inputPtc, dummy, camera, inputDims,
                     pars[fitter.par_indices["temperature_coeff"]],
                 ))
                 polyFitErr = np.zeros_like(polyFit)
-                chiSq = np.nan
+                chiSq = linearityChisq
 
                 # Update mask based on what the fitter rejected.
                 mask = fitter.mask

diff --git a/python/lsst/cp/pipe/utils.py b/python/lsst/cp/pipe/utils.py
@@ -1242,6 +1242,31 @@ def mask(self):
     def good_points(self):
         return self.mask.nonzero()[0]
 
+    def compute_chisq_dof(self, pars):
+        """Compute the chi-squared per degree of freedom for a set of pars.
+
+        Parameters
+        ----------
+        pars : `np.ndarray`
+            Parameter array.
+
+        Returns
+        -------
+        chisq_dof : `float`
+            Chi-squared per degree of freedom.
+        """
+        resids = self(pars)[0: len(self.mask)]
+        chisq = np.sum(resids[self.mask]**2.)
+        dof = self.mask.sum() - self.ngroup
+        if self._fit_temperature:
+            dof -= 1
+        if self._fit_offset:
+            dof -= 1
+        if self._fit_weights:
+            dof -= 2
+
+        return chisq/dof
+
     def __call__(self, pars):
 
         ratio_model, spl = self.compute_ratio_model(

diff --git a/tests/test_linearity.py b/tests/test_linearity.py
@@ -399,6 +399,9 @@ def _check_linearity_spline(
                 atol=resid_atol,
             )
 
+            # Loose check on the chi-squared.
+            self.assertLess(linearizer.fitChiSq[amp_name], 2.0)
+
             # If we apply the linearity correction, we should get the true
             # linear values out.
             image = lsst.afw.image.ImageF(len(mu_values), 1)