In fact, I haven't written information about the command fec
fec is used to plot contour level of a function defined
on a mesh constituted of triangles
and assuming that f is linear on triangles

The best way to undersantd how it works is to look at the two demo
files in demos/fec ( and source code for fec in routines/graphics/Fec )

===================================================================
fec.ex1 is a simple demo file in which a mesh and a function
on that mesh is completely built in Scilab syntax

Fec is used as folows :
    let no be the number of nodes
    and Ntr the number of traiangles

fec(x,y,triangles,func,no,Ntr,strflag,legend,brect,aaint)

    x and y are two vectors of size no
         (x(i),y(i)) gives the coordinates of node i
    func is also a vector of size no :
         func(i) gives the value of the function for which we want
        the level curves.

    trianles : is a [Ntr,5] matrix
        each line of triangles specifies a triangle of the
        mesh
        triangle(j) = [number,node1,node2,node3,flag]
        node1,node2,node3 : are the number of the nodes
        which constitues triangle(j)
        number : is the number of the triangle
        flag is an integer not used in the fec function

    for the remaining arguments
    strflag,legend,brect,aint : see plot2d
===================================================================

fec.ex2 is an example for which the mesh and the function value where
computed by an external `mesh builder    (amdba type mesh) and external program
A set of macros ( provided in file fec_demos.sci) were used to read the to data files in Scilab
and plot the results