Graph of a quadric : quadrique

quadrique takes as arguments the expression of a quadric with respect to x, y, z. You may also specify the variables as a vector (second argument) or as second, third and fourth arguments.
quadrique draws this quadric.
Input :

quadrique(7*x^2+4*y^2+4*z^2+4*x*y- 4*x*z-2*y*z-4*x+5*y+4*z-18)

Output :

the drawing of the ellipsoid of equation 7*x^2+4*y^2+4*z^2+4*x*y-4*x*z-2*y*z-4*x+5*y+4*z-18=0

See also quadrique_reduite for the parametric equation of the quadric.