Cem Gormezano

Last seen: meer dan 4 jaar ago | Active since 2020

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Sparse matrix multiplication complexity and CPU time
I am multiplying two sparse matrices $A$ and $A^T$ such that I have $A^T*A$. From what I know the complexity of this operation d...

meer dan 4 jaar ago | 1 answer | 0

1

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Question

Given a vector, I would like to sample without replacement elements from it repeatedly.
Given a (m x 1) vector v , I would like to ,randomly without replacement, sample s elements from it. I know I can use randsample...

meer dan 4 jaar ago | 2 answers | 0

2

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Question

Given that A is a sparse matrix, norm(A(i,:)) takes a very long time. Why and can one do better ?
I am computing norm(A(i,:)) within a loop, where A is a sparse matrix. This seems to be a bottleneck, is there anyway to perfor...

meer dan 4 jaar ago | 3 answers | 0

3

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C = union( A,B ) is too slow. Is there any faster way given that A and B are ordered.
I have two sorted arrays A and B. I want to find the elements that are both in A and B. I am using union function, yet this seem...

meer dan 4 jaar ago | 4 answers | 0

4

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Preallocating a sparse matrix, then entering values column by column takes too much time. Is there a more efficient way ?
At the beginning of the loop, I preallocate the sparse matrix (Q) with a number of non zero values that I do not exceed within t...

meer dan 4 jaar ago | 1 answer | 0

1

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Question

Which is more efficient when applied to a sparse matrix, find or logical indexing ?
Given a sparse matrix, I would like to get its non-zero entries. I would like to know if using find function is an efficient way...

meer dan 4 jaar ago | 1 answer | 0

1

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Question

MEX/Lapack/Blas problem
I don't have technical background, I am just trying to configure a solver called Blendenpik (https://uk.mathworks.com/matlabcent...

bijna 5 jaar ago | 0 answers | 0

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Question

What is the convergence criteria used in MATLAB lsqr function ?
I am using LSQR to solve Ax = b, where A is not consistent. I know that lsqr will give me the minimum residual solution. I am wo...

bijna 5 jaar ago | 0 answers | 0

0

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Question

Does MATLAB qr function employ the SuiteSparseQR (multifrontal multithreaded sparse QR factorization) in SuiteSparse ?
I am using the function [Q,R,P] = qr(A,0) to have a rank-revealing qr factorization of sparse matrix A. I am wondering if MATLAB...

bijna 5 jaar ago | 0 answers | 0

0

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