Tensor.gate: add transpose option

Author: jcmgray

docs/changelog.md

@@ -19,6 +19,7 @@ Release notes for `quimb`.
 - HV1BP: vectorize both contraction and message initialization
 - add [`qu.plot_multi_series_zoom`](quimb.utils_plot.plot_multi_series_zoom) for plotting multiple series with a zoomed inset, useful for various convergence plots such as BP
 - add `info` option to [`tn.gauge_all_simple`](quimb.tensor.tensor_core.TensorNetwork.gauge_all_simple) for tracking extra information such as number of iterations and max gauge difffi
+- [`Tensor.gate`](quimb.tensor.tensor_core.Tensor.gate): add `transposed` option
 
 **Bug fixes:**
 

quimb/tensor/tensor_core.py

@@ -2318,18 +2318,35 @@ def gate(
         G,
         ind,
         preserve_inds=True,
+        transposed=False,
         inplace=False,
     ):
-        """Gate this tensor - contract a matrix into one of its indices without
+        r"""Gate this tensor - contract a matrix into one of its indices without
         changing its indices. Unlike ``contract``, ``G`` is a raw array and the
-        tensor remains with the same set of indices.
+        tensor remains with the same set of indices. This is like applying:
+
+        .. math::
+
+            x \leftarrow G x
+
+        or if ``transposed=True``:
+
+        .. math::
+
+            x \leftarrow x G
 
         Parameters
         ----------
         G : 2D array_like
             The matrix to gate the tensor index with.
         ind : str
             Which index to apply the gate to.
+        preserve_inds : bool, optional
+            If ``True``, the order of the indices is preserved, otherwise the
+            gated index will be left at the first axis, avoiding a transpose.
+        transposed : bool, optional
+            If ``True``, the gate is effectively transpose and applied, or
+            equivalently, contracted to its left rather than right.
 
         Returns
         -------
@@ -2359,7 +2376,11 @@ def gate(
         t = self if inplace else self.copy()
 
         ax = t.inds.index(ind)
-        new_data = do("tensordot", G, t.data, ((1,), (ax,)))
+
+        if transposed:
+            new_data = do("tensordot", G, t.data, ((0,), (ax,)))
+        else:
+            new_data = do("tensordot", G, t.data, ((1,), (ax,)))
 
         if preserve_inds:
             # gated index is now first axis, so move it to the correct position