I want to obtain the partial derivative of a piecewise function. How it is possible to calculate  the derivative in (0,0) with diff?

I should get, as answer,  a new piecewise function

with(student);
f := (x, y) -> piecewise((x, y) = (0, 0), 0, (x^3*y - x*y^3)/(y^2 + x^2));
 f := proc (x, y) options operator, arrow; piecewise((x, y) = 

    (0, 0), 0, (x^3*y-x*y^3)/(y^2+x^2)) end proc

fx := (x, y) -> diff(f(x, y), x);
fx := proc (x, y) options operator, arrow; diff(f(x, y), x) end 

   proc

fx(0, 0);
Error, (in fx) invalid input: diff received 0, which is not valid for its 2nd argument

but i obtain an error

anna rita

i would like to plot a cube with the color given by a 3 variables functions (a way to plot in R^4)

in this way the cube is the domain of the functions, its color is the value of the function, i would like to put in evidence the max min of such function

but the command that i tried to use does not work:

plots[display](plotools([cuboid]([0,0,0],[1,1,1]),trasparency=.7,colorscheme["xyzcoloring",proc(x,y,z) option operator , arrow; x^2 + y^2 - z^2 end(proc)])

thanks for your help, anna rita

Hi,

i would like to plot a graph in R^3 of a function f(n,t), where n is integer and t is real. For every t i would like to have a sequence of points. Is it possible?

thanks, anna rita