utv_gauge_residual
==================

.. py:function:: t3toolbox.backend.utv_operations.utv_gauge_residual(frame_data, variations_data)

   .. code-block:: python

      def utv_gauge_residual(
              frame_data,       # UT3Frame .data
              variations_data,  # UT3Variations .data
      ) -> NDArray:  # shape = variation stack (K+C); per stack element (scalar/0-d when unstacked)


   Max violation of the gauge conditions for a uniform tangent vector, **per stack element** (the
   uniform mirror of :py:func:`tv_operations.tv_gauge_residual`).

   Each Tucker variation must be orthogonal to its up-core (``U^T dU = 0``) and each left-interior TT
   variation orthogonal to its left-core (``(P^L)^T dG^L = 0``). Mask-once, then the gauge grams vectorized
   over ``d``, max-abs reduced over the gram axes (keeping the stack), then the max over all checks (the
   last TT core is excluded -- the ``[:-1]`` boundary). A caller thresholds it (``<= atol``).