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 However, nonspecialists (including many doctors) still tend to use an older perspective, now seen as outdated by experts.
1 Twenty-six percent of men and 17 percent of women have tried cocaine or other street drugs (not including marijuana) at some time in their life. 2  Seven percent of men and 4 percent of women had done so within the past 12 months.