From 74e9179d30e0ebdb062a734ebf6ffd1573b7d9c9 Mon Sep 17 00:00:00 2001
From: Markus Zolliker <markus.zolliker@psi.ch>
Date: Wed, 11 Mar 2026 10:00:09 +0100
Subject: [PATCH] add frappy.lib.interpolation

Change-Id: Ia1c50decc4485d9910f133a7a0de339e5d70389f
---
 frappy/lib/interpolation.py | 47 +++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 frappy/lib/interpolation.py

diff --git a/frappy/lib/interpolation.py b/frappy/lib/interpolation.py
new file mode 100644
index 00000000..f6b472de
--- /dev/null
+++ b/frappy/lib/interpolation.py
@@ -0,0 +1,47 @@
+# *****************************************************************************
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Module authors:
+#   Markus Zolliker <markus.zolliker@psi.ch>
+#
+# *****************************************************************************
+"""interpolation, mainly used for pid tables"""
+
+import numpy as np
+
+
+class Interpolation(list):
+    def __init__(self, table, logx=None, logy=None):
+        """initialize table
+
+        :param table: sequence of tuple (x, y)
+        :param logx, logy: True/False: whether to apply log for interpolation
+            None: automatic (choose log when all values are positive)
+        :return: interpolated y value
+        """
+        table = np.array(sorted(table))
+        super().__init__(table)
+        if len(table) == 0:
+            return
+        logx = table[0][0] > 0 if logx is None else logx
+        logy = min(table[:,1]) > 0 if logy is None else logy
+        self.fwd = np.log if logx else np.array
+        self.xvalues = self.fwd(table[:,0])
+        self.rev = np.exp if logy else np.array
+        self.yvalues = np.log(table[:,1]) if logy else table[:,1]
+
+    def __call__(self, x):
+        return self.rev(np.interp(self.fwd(x), self.xvalues, self.yvalues))