Derivative and first order partial derivative : diff derive deriver

diff (or derive) takes two arguments : an expression and a variable (resp a vector of the variable name) (see several variable functions in 1.50). If only one argument is provided, the derivative is taken with respect to x
diff (or derive) returns the derivative (resp a vector of derivative) of the expression with respect to the variable (resp with respect to each variable) given as second argument.
Examples :

• Compute :
  $${\frac{{\partial (x.y^2.z^3+x.y.z)}}{{\partial z}}}$$
  Input :
  diff(x*y ^2*z^3+x*y*z,z)
  Output :
  x*y^2*3*z^2+x*y
• Compute the 3 first order partial derivatives of x*y²*z³ + x*y*z.
  Input :
  diff(x*y^2*z^3+x*y,[x,y,z])
  Output :
  [y^2*z^3+y*z, x*2*y*z^3+x*z, x*y^2*3*z^2+x*y]