This document discusses using extreme computing techniques for adaptive optics systems to directly image exoplanets. It proposes using a QDWH-based partial SVD algorithm for computing the pseudoinverse required by adaptive optics systems. This algorithm uses the polar decomposition to reduce the matrix size before computing a partial SVD, improving performance over traditional full SVD methods. Results show the QDWH approach achieves up to a 4x speedup on GPUs and reaches 75% of theoretical peak performance, making it suitable for extreme adaptive optics applications seeking exoplanets.
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Extreme Computing for Extreme Adaptive Optics: The Key to Finding Life Outside our Solar System
1. Extreme Computing for Extreme Adaptive Optics:
the Key to Finding Life Outside our Solar System
H. Ltaief1, D. Sukkari1, O. Guyon2,3,4, and D. Keyes1
1Extreme Computing Research Center, KAUST, Saudi Arabia
3Steward Observatory, University of Arizona, Tucson, USA
2National Institutes of Natural Sciences, Tokyo, Japan
4National Astronomical Observatory of Japan, Subaru Telescope
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4. The Subaru Telescope
Represents a flagship telescope of the National Astronomical
Observatory of Japan
Carries a 8.2-meter (320in) diameter telescope
Contains a high-contrast imaging system for directly imaging
exoplanets
Operates perhaps the most advanced HPC facility in computational
astronomy
Lives at the Mauna Kea Observatory in Hawaii
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8. The Astronomical Challenge
Turbulence in the atmosphere limits the
performance of astronomical telescopes
Without active correction of such defects, images
would be blurred to approximately one arcsecond
angle
To recover the loss of angular resolution, adaptive
optics (AO) systems measure and correct
atmospheric turbulence
In the absence of optical aberrations, the telescope
should provide λ
D angular resolution (D:telescope
diameter, λ wavelength)
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9. Adaptive Optics 101
Wavefront sensor(s)
(WFS)
Measure details of
blurring from ’guide
star’ near the object
you want to observe
A real time controller
(RTC)
Processes the WFS
signals to compute
the control matrix
based on the pseudo
inverse
Light from both guide
star and astronomical
object is reflected
from deformable
mirror; distortions are
removed
https : //www.uniдe.ch/sciences/astro/index .php/download_f ile/view/34/168/
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11. And Here Comes the Linear Algebra...
Compute the pseudo inverse A+
AA+
A = A ,A ∈ Rm×n
(m ≥ n)
The numerical challenge of the pseudo inverse are twofold:
Numerical: dealing with rectangular matrix which may engender
numerical instabilities
A A = V ΛV
Computational: high algorithmic complexity, it should still be able to
keep up with the overall throughput of the AO framework
Using SVD: A = U ΣV then:
A+
= V Σ−1
U
Only most significant singular values with their associated singular
vectors are required (≈10%)
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17. What is The Polar Decomposition?
The polar decomposition:
A = UpH , A ∈ Rm×n
(m ≥ n),
where Up is an orthogonal matrix and H =
√
A A is a symmetric positive
semidefinite matrix
The polar decomposition is a critical numerical algorithm for various
applications, including aerospace computations, chemistry, factor
analysis
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18. QDWH Polar Decomposition Algorithm
The QR-Dynamically Weighted Halley iterations:
X0 = A/α,
√
ckXk
I
=
Q1
Q2
R, Xk+1 =
bk
ck
Xk +
1
√
ck
ak −
bk
ck
Q1Q2
, k ≥ 0
The iterative procedure converges:
A = UpH,
where, UpUp = In, H is symmetric positive semidefinite
Backward stable algorithm for computing the polar decomposition
Based on conventional computational kernels, i.e., Cholesky/QR
factorizations (≤ 6 iterations for double precision) and GEMM
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19. Numerical Algorithm
Algorithm 1 Pseudo-Inverse using the QDWH-Based Partial SVD.
Compute the polar decomposition A = UpH using QDWH
Calculate [Q R] = QR(Up + Id)
Find the index ind = min(f ind(abs(diaд(R)) < threshold))
Extract ˜Q = Q(:,ind : end)
Reduce the original matrix problem ˜A = A × ˜Q
Compute the SVD of the reduced matrix problem ˜A = U Σ ˜VT
Compute the right singular vectors V = ˜QT × ˜V
Calculate the pseudo-inverse A+ = V Σ−1UT
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20. Algorithmic Complexity
Standard QDWH-based QDWH-based
SVD Full SVD Partial SVD
QDWH: (4+1/3)Nn3 x #itChol
Algorithmic 22Nn3 43Nn3 QR and GEMM: 4/3Nn3 + 2sNn2 + 2Nns2
complexity SVD: 22s3
Where, Nn is the matrix size, and s is the number of the selected singular values/vectors
(s << Nn)
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22. Environment Settings
Software:
GCC compilers
MAGMA v2.3 and CUDA v9.0 (including cuBLAS)
Single precision (SP) arithmetics is used
Ill-conditioned matrices generated using SLATMS MAGMA routine
Hardware:
The K80 GPU:
12GB of memory,
Two-socket 14-core system
Intel Broadwell system with 128GB of main memory
The P100 and V100 GPUs:
16GB of memory
Two-socket 16-core system
Intel Haswell systems with 128GB of main memory
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32. Conclusion and Future Work
Comprehensive accuracy/performance analysis of a novel
QDWH-based partial SVD algorithm
Significant performance improvement of the QDWH-based partial
SVD: up to 5X and 4X against state-of-the-art implementations on
synthetic ill-conditioned matrices and real datasets across various
hardware technologies
The pseudo inverse simulation code has been deployed at the Subaru
telescope and operating since June 24th 2018!
Future work includes:
Asynchronous task-based QDWH-based partial SVD implementation
Multi-GPUs QDWH-based partial SVD implementation
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33. Acknowledgments
Yuji Nakatsukasa, National Institute of Informatics @ Tokyo, Japan
NVIDIA GPU Research Center
Cray Center of Excellence
Intel Parallel Computing Center
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34. The World’s Biggest Eye on The Sky
Credits: ESO (http://www.eso.org/public/teles-instr/e-elt/)
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35. The World’s Biggest Eye on The Sky
Credits: ESO (http://www.eso.org/public/teles-instr/e-elt/)
The largest optical/near-infrared telescope in the world.
It will weigh about 2700 tons with a main mirror diameter of 39m.
Location: Chile, South America.
H. Ltaief et al., Real-Time Massively Distributed Multi-Object Adaptive Optics
Simulations for the European Extremely Large Telescope, IEEE IPDPS 2018: designing
one of the most challenging instruments (MOSAIC)
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36. Exciting Time for Astronomy at KAUST/ECRC!
Supporting two major worldwide ground-based astronomy efforts
The E-ELT Telescope The Subaru Telescope
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37. Bringing Astronomy Back Home ;-)
Courtesy from CEMSE Communications, KAUST
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40. Moving Forward with Extreme AO
Last N WFS
measurements
sensor 1
N x n
Last N WFS
measurements
sensor K
N x n
MVM
Last N WFS
measurements
N x n
MVM
Last WFS
measurement
n
MVM
DM state
m
DM state
m
DM state
m
Control Matrix
m x n
Predictive Control Matrix
m x ( N x n )
Sensor Fusion and
Predictive control Matrix
m x ( K x N x n )
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