Linear transforms

They are defined using the command transform_lin. They can act only on vectors, using the command act, and can be used to define affine transforms. In

 - funct -> transform_lin Tlin
 - funct -> coord_lin Tlin 1 2 3 4

the first command defines a linear transform Tlin. The second instruction defines its matrix : $\pmatrix{{\tt 1} & {\tt 2}\cr {\tt 3} & {\tt 3}}$ .