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For questions about construction and modification of matrices, objects represented by 2-dimensional arrays that are used to define linear operators within linear algebra.

3 votes

Strassen Algorithm for Unusal Matrices

If I gave you two 1025 x 1025 matrices, you wouldn't extend them to 2048 x 2048. … For non-square matrices: If you want to multiply a (100x100) by a (1000x100) matrix, that can be done trivially by calculating ten (100x100) x (100x100) products. …
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1 vote
Accepted

Prove Permutation approach of finding best paranthesization to matrix chain multiplication i...

What people often forget: They have a problem, and the have a sub problem that helps solving the problem. And then they try solving the (hard) sub problem - without realising there is a much better so …
gnasher729's user avatar
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1 vote

In Strassen's algorithm, why does padding the matrices with zeros not affect the asymptopic ...

You can take any matrix with N/2 < n < N rows and columns, pad it, and multiply it with Strassen's algorithm (or the naive algorithm for example), and then drop lots of zeroes that were created by the …
gnasher729's user avatar
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2 votes

How much can matrix multiplication algorithm be parallelized?

Ypu're starting from a completely wrong point. The execution time of matrix multiplication does not come from the number of multiplications and additions, it's the number of uncached memory accesses …
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5 votes

Fastest way to solve a system of linear equations

There is what you want to achieve, and there is reality, and sometimes they are in conflict. First you check if your problem is a special case that can be solved quicker, for example a sparse matrix. …
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6 votes

In algorithms for matrix multiplication (eg Strassen), why do we say n is equal to the numbe...

If we let $m = 2n^2$, that is the total number of elements in both matrices, then it is $m^{1.5} / 2^{1.5}$ multiplications and $m^{1.5} / 2^{1.5} - m/2$ additions. … are needed, depending on the shapes of the matrices. …
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5 votes

Arrays. Find row with most 1's, in O(n)

Hint: If the first row has k 1s, and the second row has k’ 1s, then there is no need to determine k’ at all if k’ <= k. How do you find in O(1) that k’ <= k? And if k’ > k, which you checked in O(1), …
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5 votes
Accepted

Are there parallel matrix exponentiation algorithms that are more efficient than sequential ...

Given these four results and the original M, you can calculate four of the matrices $M^6$ to $M^{25}$ in the same time again, provided the matrices are at most five powers apart from each other. … With these matrices calculated, all matrices up to $M^{108}$ and some more up to $M^{125}$ can be calculated in three times the time of a single matrix product if four processors are available. …
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1 vote

Running time of sparse matrix multiplication

The question doesn't make any sense. It doesn't make sense to ask for the running time of a computation, unless you specify an algorithm for that computation. So how would you calculate this product? …
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0 votes

Is order of matrix multiplication affecting numerical accuracy of the result?

Interesting problem. Obviously with floating point involved, you can’t expect the same results, but we’d like to know what tended to give better results? In a completely unscientific way, you can per …
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