This process is illustrated in the adjacent picture. Here formula_5 is assumed to be defined on the plane, and that its graph has a bowl shape. The blue curves are the contour lines, that is, the regions on which the value of formula_5 is constant. A red arrow originating at a point shows the direction of the negative gradient at that point. Note that the (negative) gradient at a point is orthogonal to the contour line going through that point. We see that gradient "descent" leads us to the bottom of the bowl, that is, to the point where the value of the function formula_5 is minimal.