Definition has the following format:
F(x,y)
where
F(x,y) – is an expression which (after calculations), contains only variables, corresponding to the coordinate axes. By default, variables names are x and y.
The graph of this type is presented with a set of short strokes, having slope equal to value of the function F(x,y) at points, corresponding to the middle of each stroke. Graphs of this types are used for qualitative analysis of ordinary differential equations.
Example:
x/y ; directional field, tangent to integral curves of equation y’=x / y