I have two multivariate functions $f_1(x,y)$ and $f_2(x,y)$. I want a plot in which in the horizontal axis I have the values of $f_1$ in a specific point $(a,b)$ and on the vertical axis I have the value of $f_2$ in the same point $(a,b)$. I tried storing the values of the functions in two lists and plot them, but it would be nice to be able to avoid this solution.