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 However, nonspecialists (including many doctors) still tend to use an older perspective, now seen as outdated by experts.
When people develop an addiction, they can experience irritability and restlessness when they try to stop marijuana use. They can develop deep cravings for marijuana that can interrupt their sleep, their work, and their hobbies. This is another hallmark of addiction, and itâs a known risk with marijuana use.