# Getting Started with OpenSees -- Model Builder

### From OpenSeesWiki

Defining the model builder using the OpenSees model command expands the Tcl command library to include OpenSees-specific commands, such as node and element definition, etc. Currently, there is only one model builder available, basic model builder, this is the model builder that includes all the commands presented in this library.

The model builder also defines the number of dimensions (ndm) and degrees of freedom per node (ndf):

*model BasicBuilder -ndm $ndm <-ndf $ndf>*

For a 2-D problem, you really only need three degrees of freedom at each node, the two translations in the plane and the rotation about the plane's normal:

- model basic -ndm 2 -ndf 3

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