Drawing the graph of an relation with r and θ
By inputting an relation with an expression using r and θ, you can draw the graph of the polar equation.
You can use x and y in an expression at the same time.
Because the parameter θ is dealt with as an argument in the relation, θ in the relation cannot be substituted by a value.
The graph will not be sometimes correctly drawn, if the funcion has discontinuities.
[The hot skinny of GRAPES]
r = Sqrt (x2 + x2), θ = arg (x, y). "arg" is a function which gives an argument and takes a value from 0 to 2π or from -π to π. Because of this, when a point (x, y) moves across the x axis, the value of arg (x, y) changes discontinously and the graph of function will not be sometimes correctly drawn.