docstr: Estimate motion parameters at a particular time.
docstr_tok: ["Estimate","motion","parameters","at","a","particular","time","."]
code: def estimate_instant_motion(self, t):
      """
      Estimate motion parameters at a particular time.
      """
      if VERBOSE:
          print(
              "Estimating motion at time frame %d/%d..."
              % (t + 1, self.nscans)
          )
  
      def f(pc):
          self._init_energy(pc)
          return self._energy()
  
      def fprime(pc):
          self._init_energy(pc)
          return self._energy_gradient()
  
      def fhess(pc):
          self._init_energy(pc)
          return self._energy_hessian()
  
      self.init_instant_motion(t)
      fmin, args, kwargs = configure_optimizer(
          self.optimizer,
          fprime=fprime,
          fhess=fhess,
          **self.optimizer_kwargs,
      )
  
      # With scipy >= 0.9, some scipy minimization functions like
      # fmin_bfgs may crash due to the subroutine
      # `scalar_search_armijo` returning None as a stepsize when
      # unhappy about the objective function. This seems to have the
      # potential to occur in groupwise registration when using
      # strong image subsampling, i.e. at the coarser levels of the
      # multiscale pyramid. To avoid crashes, we insert a try/catch
      # instruction.
      try:
          pc = fmin(
              f, self.transforms[t].param, disp=VERBOSE, *args, **kwargs
          )
          self.set_transform(t, pc)
      except:
          warnings.warn("Minimization failed")
  
imports: import os
  import warnings
  import numpy
  from nibabel import io_orientation
  from nibabel.affines import apply_affine
  from ...core.image.image_spaces import as_xyz_image, make_xyz_image, xyz_affine
  from ...io.nibcompat import get_header
  from ..slicetiming import timefuncs
  from ._registration import _cspline_sample3d, _cspline_sample4d, _cspline_transform
  from .affine import Affine, Rigid
  from .optimizer import configure_optimizer, use_derivatives
  from .type_check import check_type, check_type_and_shape
label_desc: Use image node_id 11 for calling the Realign4dAlgorithm obj's underlying member method code with example usage: obj.estimate_instant_motion(t) and returns: self, self, self