Despite the fact, that this question might not be of interest anymore...
To plot a tensor, you first have to rotate it to its eigenvectors.
For this, you can solve the eigenvalue problem and get as results the eigenvalues (gives information for the radius of the ellipsoid in the main spatial directions (x, y & z)) and the eigenvectors (gives information on how you need to rotate the ellipsoid).
[Vec, Val] = eig(F);
So to generate the plot, you first calculate the ellipsiods surface when centered and not rotated. xc, yc and zc set to zero (center of ellipsoid) and xr, yr and zr set to the values from the eigenvalue problem.
[X,Y,Z] = ellipsoid(xc,yc,zc,xr,yr,zr);
You then can use the eigenvectors of the eigenvalue problem as rotation matrix to rotate the coordinates in the variables X, Y & Z (concatenate & reshape the matrices).
After that, you simply plot the ellipsoid:
surf(Xrot,Yrot,Zrot);
axis equal
