Finite Element Analysis. Barna Szabó

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      In the special case when α is an integer and then .

Exercise 1.19 Show how eq. (1.106) is obtained from eq. (1.105). Provide details.

Example 1.10 Let us consider model problems in the form of eq. (1.103) with the following data: , , and exact solutions in the form of eq. (1.104) corresponding to . We will use a sequence of uniform finite element meshes with and assigned to all elements. We are interested in the relationship between the estimated and true relative errors. The computed values of the potential energy and their estimated limit values computed by means of eq. (1.99) are listed in Table 1.3. These are comparable to the exact values of the potential energy listed in Table 1.2. The estimated limit values of the potential energy are denoted by .

With the information provided in Tables 1.2 and 1.3 it is possible to compare the estimated and exact values of the relative error. For example, using eq. (1.100) and

Table 1.3 Example: Computed and estimated values of the potential energy

. Uniform mesh refinement, for all elements.

	N
10	19	−2.17753673	−1.73038992	−1.41382648	−1.17955239
100	199	−2.25079984	−1.74673700	−1.41675042	−1.17984996
1000	1999	−2.29589857	−1.75303348	−1.41745363	−1.17989453
		−2.37254083	−1.75716094	−1.41768637	−1.17990276

the estimated relative error in energy norm for , is:

      or 5.22%. When using the exact value of the potential energy for reference then the relative error is the same as the estimated relative error to within three digits of accuracy:

      Exercise 1.20 Compare the estimated and exact values of the relative error in energy norm for the problem in Example

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