Accuracy Verification Methods: Theory and Algorithms by Olli Mali

By Olli Mali

The significance of accuracy verification equipment was once understood on the very starting of the advance of numerical research. fresh many years have noticeable a speedy development of effects regarding adaptive numerical tools and a posteriori estimates. even if, during this vital quarter there usually exists a visible hole among mathematicians growing the idea and researchers constructing utilized algorithms which may be utilized in engineering and clinical computations for assured and effective mistakes control.

The objectives of the e-book are to (1) supply a clear clarification of the underlying mathematical idea in a mode available not just to complicated numerical analysts but in addition to engineers and scholars; (2) current distinct step by step algorithms that stick to from a thought; (3) speak about their benefits and disadvantages, parts of applicability, provide concepts and examples.

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1, we present the estimates obtained by minimizing y for k iteration steps. The efficiency index of the majorant is defined by the formula Ieff := M2 (v, y, β) |u − v | . For comparison, on the bottom line we also present the values obtained by substituting the exact flux p to the majorant. 17). 17). 1, the majorant provides a guaranteed upper bound. Moreover, the bound becomes sharper if we invest more to the computation of a suitable y. It is easy to see that the parts of the majorant (as well as the whole majorant) converges toward the values obtained by substituting p (actually, one can show that p is the exact minimizer of the majorant).

3 Error Indicators for Goal-Oriented Quantities 35 Note that ∇(uhref − uh ) 2 2 = ∇(uhref − uh ) +2 Ω + ∇(uh − uh ) 2 ∇(uhref − uh ) · ∇(uh − uh ) dx. 55) and obtain ∇(uhref − uh ) 2 ≥ ∇ wh 2 + ∇(uh − uh ) 2 − 2γ ∇ wh ∇(uh − uh ) ≥ 1 − γ 2 ∇ wh 2 . 59), we find that ∇ wh 2 ≤ 1 ∇(uhref − uh ) 1−γ2 2 = 1 1−γ2 ∇ wh · ∇ wh dx. 59). We have ∇(u − uh ) 2 2 1 ∇ wh . 61) + ∇(uh − uhref ) 2 and use ∇ wh · wh dx Ω ≤ λ2 ∇(u − uh ) 2 + ∇ wh ≤ λ2 ∇(u − uh ) 2 + ∇ wh 1 ∇ wh 2 . 62) ∇ wh and motivates using ∇ wh as an error indicator.

At each step of this procedure the value of div y + f 2Ω decreases. After several cycles of minimization we obtain a vector-valued field, which is equilibrated much better than the original one. 5 Global Averaging In many cases, an efficient averaging operator is obtained if local minimization problems on patches are replaced by a global problem (this method may generate essential computational expenditures). Consider the following problem: Find g¯ h in a certain (global) set Uh (Ω), which minimizes the quantity i Ti |gh − ∇uh |2 dx among all gh ∈ Uh (Ω).

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