some additional information about pinv

theano/sandbox/linalg/ops.py

@@ -484,6 +484,11 @@ class MatrixPinv(Op):
     :math:`A^+` is that matrix such that :math:`\bar{x} = A^+b`.
 
     Note that :math:`Ax=AA^+b`, so :math:`AA^+` is close to the identity matrix.
+    This method is not faster then `matrix_inverse`. Its strength comes from
+    that it works for non-square matrices.
+    If you have a square matrix though, `matrix_inverse` can be both more
+    exact and faster to compute. Aslo this op does not get optimized into a
+    solve op.
     """
     def __init__(self):
         pass