305 research outputs found
Sparse Allreduce: Efficient Scalable Communication for Power-Law Data
Many large datasets exhibit power-law statistics: The web graph, social
networks, text data, click through data etc. Their adjacency graphs are termed
natural graphs, and are known to be difficult to partition. As a consequence
most distributed algorithms on these graphs are communication intensive. Many
algorithms on natural graphs involve an Allreduce: a sum or average of
partitioned data which is then shared back to the cluster nodes. Examples
include PageRank, spectral partitioning, and many machine learning algorithms
including regression, factor (topic) models, and clustering. In this paper we
describe an efficient and scalable Allreduce primitive for power-law data. We
point out scaling problems with existing butterfly and round-robin networks for
Sparse Allreduce, and show that a hybrid approach improves on both.
Furthermore, we show that Sparse Allreduce stages should be nested instead of
cascaded (as in the dense case). And that the optimum throughput Allreduce
network should be a butterfly of heterogeneous degree where degree decreases
with depth into the network. Finally, a simple replication scheme is introduced
to deal with node failures. We present experiments showing significant
improvements over existing systems such as PowerGraph and Hadoop
Fast and Reliable Autonomous Surgical Debridement with Cable-Driven Robots Using a Two-Phase Calibration Procedure
Automating precision subtasks such as debridement (removing dead or diseased
tissue fragments) with Robotic Surgical Assistants (RSAs) such as the da Vinci
Research Kit (dVRK) is challenging due to inherent non-linearities in
cable-driven systems. We propose and evaluate a novel two-phase coarse-to-fine
calibration method. In Phase I (coarse), we place a red calibration marker on
the end effector and let it randomly move through a set of open-loop
trajectories to obtain a large sample set of camera pixels and internal robot
end-effector configurations. This coarse data is then used to train a Deep
Neural Network (DNN) to learn the coarse transformation bias. In Phase II
(fine), the bias from Phase I is applied to move the end-effector toward a
small set of specific target points on a printed sheet. For each target, a
human operator manually adjusts the end-effector position by direct contact
(not through teleoperation) and the residual compensation bias is recorded.
This fine data is then used to train a Random Forest (RF) to learn the fine
transformation bias. Subsequent experiments suggest that without calibration,
position errors average 4.55mm. Phase I can reduce average error to 2.14mm and
the combination of Phase I and Phase II can reduces average error to 1.08mm. We
apply these results to debridement of raisins and pumpkin seeds as fragment
phantoms. Using an endoscopic stereo camera with standard edge detection,
experiments with 120 trials achieved average success rates of 94.5%, exceeding
prior results with much larger fragments (89.4%) and achieving a speedup of
2.1x, decreasing time per fragment from 15.8 seconds to 7.3 seconds. Source
code, data, and videos are available at
https://sites.google.com/view/calib-icra/.Comment: Code, data, and videos are available at
https://sites.google.com/view/calib-icra/. Final version for ICRA 201
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