Unformatted text preview: r estimates in local
(elemental) norms may also provide an indications as to where solution accuracy is
insu cient and where re nement is needed.
A posteriori error estimates can roughly be divided into four categories.
1. Residual error estimates. Local nite element problems are created on either an
element or a subdomain and solved for the error estimate. The data depends on
the residual of the nite element solution.
2. Flux-projection error estimates. A new ux is calculated by post processing the
nite element solution. This ux is smoother than the original nite element ux
and an error estimate is obtained from the di erence of the two uxes.
3. Extrapolation error estimates. Two nite element solutions having di erent orders
or di erent meshes are compared and their di erences used to provide an error
4. Interpolation error estimates. Interpolation error bounds are used with estimates
of the unknown constants.
The four techniques are not independent but have many similarities. Surveys of error estimation procedures 7, 2...
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