CS267 - Lecture 3: Linear Algebra Optimization

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Questions and Answers

What was the world's record for matrix multiplication complexity in terms of big-O notation?

  • O(n^2.37548) (correct)
  • O(n^2.81)
  • O(n^2.37293)
  • O(n^2+ε)

Who achieved a new record for matrix multiplication complexity by reducing it from 2.37548 to 2.37293?

  • Alman and Williams
  • Jacob Scott
  • Coppersmith & Winograd
  • Virginia Vassilevska Williams (correct)

What did Lebeck mention as a possible extension for the communication lower bound?

  • Ω(n^2.81 / M^0.4) (correct)
  • Ω(n^2.37548)
  • Ω(n log^2 7 / M(log^2 7)/2 – 1)
  • Ω(n^2+ε)

Who suggested the possibility of an O(n^2+ε) algorithm?

<p>Jacob Scott (B)</p> Signup and view all the answers

Which algorithm reduced the world's record of matrix multiplication complexity to 2.37286?

<p>Alman and WIlliams (B)</p> Signup and view all the answers

What is the main focus of the given text?

<p>Achieving optimal algorithms for array operations (A)</p> Signup and view all the answers

In the context of the text, what does 'Ax=b' refer to?

<p>Solving a system of linear equations (B)</p> Signup and view all the answers

What is a key factor in determining the number of words moved according to the General Communication Lower Bound Thm?

<p>The number of iterations in the program (C)</p> Signup and view all the answers

What type of linear program is used to minimize the value of sHBL in the General Communication Lower Bound Thm?

<p>Linear programming (B)</p> Signup and view all the answers

What is the role of projections φj in determining the Communication Lower Bound Thm?

<p>Calculating the number of words moved in memory (C)</p> Signup and view all the answers

Which recent mathematical result is crucial for proving the General Communication Lower Bound Thm?

<p>'Hölder-Brascamp-Lieb (HBL)' inequality generalization (D)</p> Signup and view all the answers

What is the main focus of the lecture on 'Applications of Parallel Computing'?

<p>Communication between main memory and cache (A)</p> Signup and view all the answers

In the context of communication lower bound, what is referred to as the most expensive operation?

<p>Moving data between processors over a network (B)</p> Signup and view all the answers

For the n-body algorithm, what does the term 'array of structures' refer to?

<p>An array representing the position and charge of particles (A)</p> Signup and view all the answers

In the context of n-body data access, what does 'access A(3), B(5)' imply?

<p>Reading data entries from arrays A and B at indexes 3 and 5 (B)</p> Signup and view all the answers

What is the maximum number of loop iterations that can be done if only 10 entries of A(i) and B(j) can be accessed?

<p>25 (D)</p> Signup and view all the answers

What is the purpose of optimizing tiling in the usual n-body algorithm?

<p>To minimize data access patterns for improved performance (B)</p> Signup and view all the answers

'Optimal tiling (M=10)' in the usual n-body algorithm involves reading how many entries of A and B?

<p>10 entries of A and 5 entries of B (D)</p> Signup and view all the answers

'C = A*B' in the context of linear algebra represents what operation?

<p>'C' equals 'A' multiplied by 'B' (B)</p> Signup and view all the answers

'Communication Lower Bound on C = AꞏB' focuses on minimizing communication by limiting access to how many entries of A, B, and C in cache?

<p>'M^2' entries each (B)</p> Signup and view all the answers

'# loop iterations doable with M words of data' is represented by which formula in the context of communication lower bound?

<p>#cubes ≤ (M · M · M)^(1/2) = M^(3/2) (B)</p> Signup and view all the answers

What is the purpose of synchronization in parallel computing, as mentioned in the text?

<p>To impose order constraints and protect shared data access (D)</p> Signup and view all the answers

In the context of parallel computing, what does the term 'critical region' refer to?

<p>A section of code where thread synchronization is enforced (C)</p> Signup and view all the answers

What does the OpenMP directive 'barrier' primarily facilitate in parallel computing?

<p>Ensuring that all threads reach a common synchronization point (D)</p> Signup and view all the answers

What does 'Mutual exclusion' aim to achieve in parallel computing?

<p>Preventing multiple threads from accessing the same critical region simultaneously (D)</p> Signup and view all the answers

What role does 'omp_get_thread_num()' play in achieving synchronization in parallel computing?

<p>Assigning unique identifiers to each thread for proper ordering (B)</p> Signup and view all the answers

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