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# [Solved]: Fine-Grain parallel algorithm for LU-decomposition

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Problem Detail:

How would you understand this pseudocode of parallel algorithm for LU-decomposition ? I'm confused mostly with the

``min(i; j) - 1, ``

because I have no idea, what the author wanted to say by it. I know that it means " choose the lesser number of 'i' and 'j' and then substract one", but I don't know what is I and J here (maybe coordinates of the current task? Or is it written from the task's point of view, so the whole pseudocode runs at every task?) etc.

The whole presentation with this code (slide 12) is here.

### Pseudocode and diagram of tasks

Bigger picture here.

It will be clearer if you look at 1 slide before (10/42). The algorithm does not decide on how do you assign to node. It just says that the algorithm can be consisted of many parallel tasks. Each task has identification of \$(i,j)\$ and each executes the algorithm in slide (12/42).

More specifically, each task is assigned an entry \$a_{ij}\$ of the matrix (\$n^2\$ number of tasks), and at the end of the algorithm that entry becomes \$u_{ij}\$ if \$i \le j\$ or \$l_{ij}\$ if \$i>j\$.