Cost
Each Jacobi rotation can be done in n steps when the pivot element p is known. However the search for p requires inspection of all N ≈ ½ n2 off-diag elements. We can reduce this to n steps too if we introduce an additional index array with the property that is the index of the largest element in row i, (i = 1, …, n − 1) of the current S. Then (k, l) must be one of the pairs . Since only columns k and l change, only must be updated, which again can be done in n steps. Thus each rotation has O(n) cost and one sweep has O(n3) cost which is equivalent to one matrix multiplication. Additionally the must be initialized before the process starts, this can be done in n2 steps.
Typically the Jacobi method converges within numerical precision after a small number of sweeps. Note that multiple eigenvalues reduce the number of iterations since .
Read more about this topic: Jacobi Eigenvalue Algorithm
Famous quotes containing the word cost:
“This people must cease to hold slaves, and to make war on Mexico, though it cost them their existence as a people.”
—Henry David Thoreau (1817–1862)
“How much would it cost you to stand at the wrong end of a shooting gallery?”
—S.J. Perelman, U.S. screenwriter, Bert Kalmar, Harry Ruby, and Norman Z. McLeod. Groucho Marx, Horsefeathers, Huxley College president to con artist Baravelli (Chico Marx)
“To become a token woman—whether you win the Nobel Prize or merely get tenure at the cost of denying your sisters—is to become something less than a man ... since men are loyal at least to their own world-view, their laws of brotherhood and self-interest.”
—Adrienne Rich (b. 1929)