For a function of two variables z=f(x,y), the gradient is the two-dimensional vector <f_x(x,y),f_y(x,y)>. This definition generalizes in a natural way to functions of more than three variables. For the function z=f(x,y)=4x^2+y^2.
By this definition, about 10% of people who smoke marijuana become addicted to it. (More on Time.com: PHOTOS â Cannabis Conventions). However, nonspecialists (including many doctors) still tend to use an older perspective, now seen as outdated by experts.
Of the 11 states that appear next in line to legalize marijuana, nine surpass the nationwide rate of marijuana users. In 2012 and 2013, an estimated average of 12.3% of Americans 12 and older smoked marijuana. In Rhode Island, one of the states on our list, more than 20% had.