Solution to the problem of pre-assigned variables to 0

[compsystems]

Hello, Han, I do not propose to change the design, but to improve it, with the idea I propose it would be integrated NUM mode (HOME) with CAS MODE, since the idea is to use the same variables for example to expose a graphic analysis [PLOT], analysis numerical [NUM key] with symbolic analysis [CAS], simply defining the type of variable to symbolic (CAS mode) and then restart ([HOME MODE]).

sample:
http://www.hpmuseum.org/forum/thread-11736.html

Likewise MATLAB works, this was born as a numerical software, but they incorporated the symbolic calculation engine (Maple, then MuPAD) and everything operates very well integration between NUM / CAS mode

PHP Code:

x=-5: 0.0001: 5;
y =x .^ 3 - 3 .* x .^ 2- 9 .*x + 2 
plot (x,y),grid;
p = [1, -3, -9,2] 
r1 = roots (p);
syms x;         % assume x as symbolic var
f = x^3-3*x^2-9*x+2 
D=diff(f) % 3*x^2-6*x-9