From d6b320d43596b5f076bc015e9e6b59516227dcbc Mon Sep 17 00:00:00 2001
From: Yuchen Ethan Xiao <yx2924@columbia.edu>
Date: Mon, 18 Aug 2025 16:15:52 -0400
Subject: [PATCH 1/2] raise `ValueError` if `x_squeezed` is not strictly
 increasing

---
 news/strictly-increasing-squeeze.rst    | 23 +++++++++++++++++++++++
 src/diffpy/morph/morphs/morphsqueeze.py |  7 +++++++
 2 files changed, 30 insertions(+)
 create mode 100644 news/strictly-increasing-squeeze.rst

diff --git a/news/strictly-increasing-squeeze.rst b/news/strictly-increasing-squeeze.rst
new file mode 100644
index 00000000..f14fabf8
--- /dev/null
+++ b/news/strictly-increasing-squeeze.rst
@@ -0,0 +1,23 @@
+**Added:**
+
+* Raise ``ValueError`` if ``x_squeezed`` is not strictly increasing.
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>
diff --git a/src/diffpy/morph/morphs/morphsqueeze.py b/src/diffpy/morph/morphs/morphsqueeze.py
index bc0e4d49..4000423f 100644
--- a/src/diffpy/morph/morphs/morphsqueeze.py
+++ b/src/diffpy/morph/morphs/morphsqueeze.py
@@ -78,6 +78,13 @@ def morph(self, x_morph, y_morph, x_target, y_target):
         coeffs = [self.squeeze[f"a{i}"] for i in range(len(self.squeeze))]
         squeeze_polynomial = Polynomial(coeffs)
         x_squeezed = self.x_morph_in + squeeze_polynomial(self.x_morph_in)
+        strictly_increasing_x = (np.diff(x_squeezed) > 0).all()
+        if not strictly_increasing_x:
+            raise ValueError(
+                "Computed squeezed x is not strictly increasing. "
+                "Please change the input x_morph or the squeeze "
+                "coefficients."
+            )
         self.y_morph_out = CubicSpline(x_squeezed, self.y_morph_in)(
             self.x_morph_in
         )

From add0413994326e2e5493a796aabc8ed8e60afbbf Mon Sep 17 00:00:00 2001
From: Yuchen Ethan Xiao <yx2924@columbia.edu>
Date: Thu, 11 Sep 2025 15:58:10 -0400
Subject: [PATCH 2/2] chore: update error message

---
 src/diffpy/morph/morphs/morphsqueeze.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/diffpy/morph/morphs/morphsqueeze.py b/src/diffpy/morph/morphs/morphsqueeze.py
index 61260683..a6b0aac1 100644
--- a/src/diffpy/morph/morphs/morphsqueeze.py
+++ b/src/diffpy/morph/morphs/morphsqueeze.py
@@ -87,7 +87,8 @@ def morph(self, x_morph, y_morph, x_target, y_target):
         if not strictly_increasing_x:
             raise ValueError(
                 "Computed squeezed x is not strictly increasing. "
-                "Please change the input x_morph or the squeeze "
+                "The squeezed morph is only intended for small polynomial "
+                "stretches. Please decrease the magnitude of the polynomial "
                 "coefficients."
             )