High Quality Content by WIKIPEDIA articles! Sparse approximation is the problem of finding a signal or vector estimate with sparseness property, that is having a small number of nonzero elements, that satisfies (approximately) a system of equations. For example, consider a linear system of equations y = Ax, where A is a real M-by-N matrix and M < N. In general, this problem is ill-posed as there are infinitely many x that solve this system. One way to enforce sparsity is to choose x such...
High Quality Content by WIKIPEDIA articles! Sparse approximation is the problem of finding a signal or vector estimate with sparseness property, that is having a small number of nonzero elements, that satisfies (approximately) a system of equations. For example, consider a linear system of equations y = Ax, where A is a real M-by-N matrix and M < N. In general, this problem is ill-posed as there are infinitely many x that solve this system. One way to enforce sparsity is to choose x such that as many components as possible are zero. In other words, we want to solve min_x |x|_0, text{ such that } y = A x, where the objective function is defined by |x|_0 = #{ k : x_k neq 0, , k=1,ldots,N } and # denotes the cardinality of the set. However, this problem is NP-complete because classical combinatorial optimization can be reduced to it.
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Рассел попросил папу построить крепость на дереве. И хотя папа ни разу в жизни ничего не строил и не очень-то уверен в своих силах, он берётся за дело. Крепость получается не совсем такой, как мечталось Расселу, но всё же она очень ему нравится. Только вот на следующий день неподалёку начинается строительство другой крепости... Иллюстратор: Цинь Лэн Перевод: Анна Ремез
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