## Example 4711: Error estimation for L-shaped problem using patch fitting and bilinear elements

```A linear elastic plane stress problem is solved on an L-shaped domain using bilinear
elements. Then fields of the three components of stress (stress in x, y and shear stress)
are then fitted using the superconvergent patch recovery technique.
The percentage relative error in the strain energy norm is then computed.
```

#### The comfile run by this example is as follows:

```#Example_4711 An error estimation problem

FEM
FEM define nodes;r;L;example
FEM define window
FEM draw nodes
FEM define bases;r;example      # Defines two bilinear bases,
# one for solving the problem and one for patch fitting
FEM define elements;r;example
FEM draw lines
FEM draw elements
FEM define fibre;d
FEM define element;r;;example fibre
FEM define equation;r;example lock
FEM define material;r;example
FEM group nodes 1,8,15,22,29,33,37 as left_edge
FEM group nodes 7,14,21,28 as right_edge
FEM group nodes 37,38,39,40 as top
FEM define initial;r;example
FEM draw reactions
FEM draw nodes
FEM define solve;r;example
FEM solve
FEM draw lines deformed dotted scale 5
FEM define field;r;example  # Define 3 fields, for stress in x dirn, y dirn and shear stress
FEM define elements;r;example field
FEM define fit;r;example gauss patch
FEM update gauss stress reference components basis 2
FEM fit patch nodes 1..40 basis 2
FEM update gauss stress reference components basis 1
FEM evaluate error
FEM draw element error
refresh graphics
FEM draw field field 1
refresh graphics
FEM draw field field 2
refresh graphics
FEM draw field field 3
FEM
```

#### Files used by this example are:

```Name              Modified     Size

example_4711.com  10-Apr-2000  1.2k
l.ipbase          10-Apr-2000  2.1k
l.ipelem          10-Apr-2000  8.6k
l.ipelfb          10-Apr-2000  3.8k
l.ipelfd          10-Apr-2000  6.8k
l.ipequa          26-May-2003  1.8k
l.ipfiel          10-Apr-2000  8.5k
l.ipfit           10-Apr-2000  620
l.ipinit          10-Apr-2000  808
l.ipmate          10-Apr-2000  1.4k
l.ipnode          10-Apr-2000  5.4k
l.ipsolv          13-Apr-2007  1.0k
test_output       10-Apr-2000   43
```

```Name                           Modified     Size