I attempt to draw a 3d plot using plot3d.  The function contains a weighted combination of absolute values.  To simplify the problem statement, suppose drawing -abs(x-y) for x=-1..1, y=-1..1.  It was found that near the zero plane, the plot become sawtooth like, which is an unexpected result.  How can I remove this effect?

I encounter a situation demonstrated in the following piece of codes:

I would like to compile a Maple procedure to compute a large matrix.  However, I cannot find a way to send it back from the procedure.  Does any feasible way exist?

Thanks!

f:=proc ()
local s;
s := time();
FileTools[Text][WriteString]('default', "a");
FileTools[Flush]('default');
while time() < s+20 do  end do
end proc;
f();

In the codes above, I intended that the string "a" is outputed immediately after the function FileTools[Text][WriteString] is called.  But in execution, the output does not appear until 20 seconds elapse.

How can I force the output appear immediately?

I am going to simplify the following formula:

sqrt(a^2*p*(1-p)*(N-n)/(n^2*(N-1)))

I wrote simplify(sqrt(a^2*p*(1-p)*(N-n)/(n^2*(N-1))),symbolic), the output was: