description:
isConvex = NCisConvex(f) checks if the polynomial f is convex without SDP.
arguments:
f is an NCpoly representing a polynomial
output:
isConvex equals 1 if the polynomial f is convex and 0 otherwise
possible usage:
NCisConvex(f)
example:
>> isConvex=NCisConvex(x^2+x*y+y*x+2*y^2+z^2-1)
isConvex = 1