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## 4.1  FE mesh declaration

This section gives a summary of FE mesh declaration with pointers to more detailed documentation.

### 4.1.1  Direct declaration of geometry (truss example)

Hand declaration of a model can only be done for small models and later sections address more realistic problems. This example mostly illustrates the form of the model data structure.

The geometry is declared in the model.Node matrix (see section 7.1 and section 7.1.1). In this case, one defines 6 nodes for the truss and an arbitrary reference node to distinguish principal bending axes (see beam1)

``` %     NodeID  unused   x y z
model.Node=[ 1      0 0 0    0 1 0; ...
2      0 0 0    0 0 0; ...
3      0 0 0    1 1 0; ...
4      0 0 0    1 0 0; ...
5      0 0 0    2 0 0; ...
6      0 0 0    2 1 0; ...
7      0 0 0    1 1 1]; % reference node
```

The model description matrix (see section 7.1) describes 4 longerons, 2 diagonals and 2 battens. These can be declared using three groups of beam1 elements

``` model.Elt=[ ...
% declaration of element group for longerons
Inf     abs('beam1') ; ...
%node1  node2   MatID ProID nodeR, zeros to fill the matrix
1       3      1    1     7       0 ; ...
3       6      1    1     7       0 ; ...
2       4      1    1     7       0 ; ...
4       5      1    1     7       0 ; ...
% declaration of element group for diagonals
Inf     abs('beam1') ; ...
2       3      1    2     7       0 ; ...
4       6      1    2     7       0 ; ...
% declaration of element group for battens
Inf     abs('beam1') ; ...
3       4      1    3     7       0 ; ...
5       6      1    3     7       0 ];
```

You may view the declared geometry

``` cf=comgui('guifeplot -project "SDT Root"',3); % Robust open in figure(3)
cf.model=model;       % create feplot axes
fecom(';view2;textnode;triax;'); % manipulate axes
```

The demo_fe script illustrates uses of this model.