Function: deriv
Section: polynomials
C-Name: deriv
Prototype: GDn
Help: deriv(x,{v}): derivative of x with respect to v, or to the main
 variable of x if v is omitted.
Doc:
 derivative of $x$ with respect to the main
 variable if $v$ is omitted, and with respect to $v$ otherwise. The derivative
 of a scalar type is zero, and the derivative of a vector or matrix is done
 componentwise. One can use $x'$ as a shortcut if the derivative is with
 respect to the main variable of $x$.

 By definition, the main variable of a \typ{POLMOD} is the main variable among
 the coefficients from its two polynomial components (representative and
 modulus); in other words, assuming a polmod represents an element of
 $R[X]/(T(X))$, the variable $X$ is a mute variable and the derivative is
 taken with respect to the main variable used in the base ring $R$.
