Issue #29 moved ave and ddx to utils.

SimPEG/utils/__init__.py

@@ -6,6 +6,6 @@ import ModelBuilder
 import Solver
 from Solver import Solver
 from matutils import getSubArray, mkvc, ndgrid, ind2sub, sub2ind
-from sputils import spzeros, kron3, speye, sdiag
+from sputils import spzeros, kron3, speye, sdiag, ddx, av
 from lomutils import volTetra, faceInfo, inv2X2BlockDiagonal, inv3X3BlockDiagonal, indexCube, exampleLomGird
 from interputils import interpmat

SimPEG/utils/sputils.py

@@ -20,3 +20,13 @@ def kron3(A, B, C):
 def spzeros(n1, n2):
     """spzeros"""
     return sp.coo_matrix((n1, n2)).tocsr()
+
+
+def ddx(n):
+    """Define 1D derivatives, inner, this means we go from n+1 to n"""
+    return sp.spdiags((np.ones((n+1, 1))*[-1, 1]).T, [0, 1], n, n+1, format="csr")
+
+
+def av(n):
+    """Define 1D averaging operator from cell-centres to nodes."""
+    return sp.spdiags((0.5*np.ones((n+1, 1))*[1, 1]).T, [0, 1], n, n+1, format="csr")