Topic: Incorrect graph for f(x,y)g(x,y) = 0

Hi,
Graph gives incorrect graphs for some equations of the type f(x,y) * g(x,y) = 0.
Examples:
(abs(x-1) + abs(y) - 1) * (abs(x) + abs(y-1) - 1) = 0;
(x-y) * (x-y) = 0;
(x^2 + y^2 - 1) * (x^2 + y^2 - 1) = 0.

Post's attachments

correct_graph.png, 8.5 kb, 737 x 613
correct_graph.png 8.5 kb, 610 downloads since 2011-08-11 

incorrect_graph.png, 8.24 kb, 737 x 613
incorrect_graph.png 8.24 kb, 674 downloads since 2011-08-11 

Re: Incorrect graph for f(x,y)g(x,y) = 0

I never considered this case though I new there could be some problems with the algorithm used to plot equations.

When Graph plots an equation  it converts it to f(x,y)=0 and looks for where f(x,y) changes sign. The problem with an equation like (x-y)*(x-y)=0 is that (x-y)*(x-y) is always positive and never changes sign. Wherefore Graph doesn't find the place where it becomes 0.

I am planning to implement a better algorithm in Graph 4.5, which should solve this problem.