Optimal algorithms for parallel Givens factorization on a coarse-grained PRAM

We study the complexity of the parallel Givens factorization of a square matrix of size n on a shared memory architecture composed with p identical processors (coarse grained EREW PRAM). We show how to construct an asymptotically optimal algorithm. We deduce that tje time complexity is equal to: ... (formule)... and that the minimum number of processors in order to compute the Givens factorization in asymptotically optimal time (2n + o(n)) is equal to p opt = n/(2 + √2) + o(n). These results complete previous analysis presented in the case where the number of processors is unlimited