From fbe0b714de5450c126adef776bcea3961b0410d7 Mon Sep 17 00:00:00 2001
From: domfournier <dominiquef@mirageoscience.com>
Date: Fri, 28 Feb 2025 14:36:35 -0800
Subject: [PATCH 1/2] Bring back Projection as input for Wires

---
 simpeg/maps/_base.py | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/simpeg/maps/_base.py b/simpeg/maps/_base.py
index b2d0def858..cd3336b10b 100644
--- a/simpeg/maps/_base.py
+++ b/simpeg/maps/_base.py
@@ -1140,20 +1140,24 @@ def __init__(self, *args):
                 and isinstance(arg[0], str)
                 and
                 # TODO: this should be extended to a slice.
-                isinstance(arg[1], (int, np.integer))
+                isinstance(arg[1], (int, np.integer, Projection))
             ), (
-                "Each wire needs to be a tuple: (name, length). "
+                "Each wire needs to be a tuple: (name, length) or (name, Projection). "
                 "You provided: {}".format(arg)
             )
 
-        self._nP = int(np.sum([w[1] for w in args]))
         start = 0
         maps = []
         for arg in args:
-            wire = Projection(self.nP, slice(start, start + arg[1]))
+
+            if isinstance(arg[1], (int, np.integer)):
+                wire = Projection(self.nP, slice(start, start + arg[1]))
+                start += arg[1]
+            else:
+                wire = arg[1]
+
             setattr(self, arg[0], wire)
             maps += [(arg[0], wire)]
-            start += arg[1]
         self.maps = maps
 
         self._tuple = namedtuple("Model", [w[0] for w in args])

From e0adeaff5de0307d3860443d3ffa29489e42cc87 Mon Sep 17 00:00:00 2001
From: domfournier <dominiquef@mirageoscience.com>
Date: Fri, 28 Feb 2025 14:39:13 -0800
Subject: [PATCH 2/2] Bring back derivs

---
 simpeg/maps/_base.py | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/simpeg/maps/_base.py b/simpeg/maps/_base.py
index cd3336b10b..2671b2a87f 100644
--- a/simpeg/maps/_base.py
+++ b/simpeg/maps/_base.py
@@ -1159,8 +1159,9 @@ def __init__(self, *args):
             setattr(self, arg[0], wire)
             maps += [(arg[0], wire)]
         self.maps = maps
-
-        self._tuple = namedtuple("Model", [w[0] for w in args])
+        self._nP = maps[0][1].nP
+        self._tuple = namedtuple("Model", [name for name, _ in args])
+        self._projection = sp.vstack([wire.P for _, wire in self.maps])
 
     def __mul__(self, val):
         assert isinstance(val, np.ndarray)
@@ -1180,6 +1181,22 @@ def nP(self):
         """
         return self._nP
 
+    def deriv(self, m):
+        """
+        Derivative of the mapping with respect to the input parameters
+
+        Parameters
+        ----------
+        m : (n_param, ) numpy.ndarray
+            The model for which the gradient is evaluated.
+
+        Returns
+        -------
+        (n_param, ) numpy.ndarray
+            The Gradient of the mapping function evaluated for the model provided.
+        """
+        return self._projection
+
 
 class TileMap(IdentityMap):
     """