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Download as PDF; Printable version; ... We seek the solution to a set of linear equations, expressed in matrix terms as ... is the condition number.
The condition number with respect to L 2 arises so often in numerical linear algebra that it is given a name, the condition number of a matrix. If ‖ ⋅ ‖ {\displaystyle \|\cdot \|} is the matrix norm induced by the L ∞ {\displaystyle L^{\infty }} (vector) norm and A {\displaystyle A} is lower triangular non-singular (i.e. a i i ≠ 0 ...
In linear algebra and numerical analysis, a preconditioner of a matrix is a matrix such that has a smaller condition number than . It is also common to call T = P − 1 {\displaystyle T=P^{-1}} the preconditioner, rather than P {\displaystyle P} , since P {\displaystyle P} itself is rarely explicitly available.
The standard convergence condition (for any iterative method) is when the spectral radius of the iteration matrix is less than 1: ρ ( D − 1 ( L + U ) ) < 1. {\displaystyle \rho (D^{-1}(L+U))<1.} A sufficient (but not necessary) condition for the method to converge is that the matrix A is strictly or irreducibly diagonally dominant .
Conjugate gradient, assuming exact arithmetic, converges in at most n steps, where n is the size of the matrix of the system (here n = 2). In mathematics, the conjugate gradient method is an algorithm for the numerical solution of particular systems of linear equations, namely those whose matrix is positive-semidefinite.
The matrix X is subjected to an orthogonal decomposition, e.g., the QR decomposition as follows. = , where Q is an m×m orthogonal matrix (Q T Q=I) and R is an n×n upper triangular matrix with >. The residual vector is left-multiplied by Q T.
It would be good to reduce the condition number of A. This can be done by preconditioning : A matrix P such that P ≈ A −1 is constructed, and then the equation PAx = Pb is solved for x . Using the exact inverse of A would be nice but finding the inverse of a matrix is something we want to avoid because of the computational expense.
Consider the system of equations x + y + 2z = 3, x + y + z = 1, 2x + 2y + 2z = 2.. The coefficient matrix is = [], and the augmented matrix is (|) = [].Since both of these have the same rank, namely 2, there exists at least one solution; and since their rank is less than the number of unknowns, the latter being 3, there are infinitely many solutions.