# use(Ring) -- install ring variables and ring operations

## Synopsis

• Function: use
• Usage:
use R
• Inputs:
• Consequences:
• All variables of R are set to global variables. Additionally, certain operations creating elements of R are installed globally.

## Description

When a ring (or a monoid) is assigned to a global variable, this function is automatically called for it.

It is possible to have several polynomial rings defined, perhaps with a variable belonging to several rings.

 i1 : R = QQ[a..d] o1 = R o1 : PolynomialRing i2 : S = QQ[b,c,d,e] o2 = S o2 : PolynomialRing i3 : b o3 = b o3 : S
At this point, b is thought to be a variable of S. If one typed a+b, an error would occur, since Macaulay2 doesn't know how to add elements of R and S together. This is fixed via:
 i4 : use R o4 = R o4 : PolynomialRing i5 : b o5 = b o5 : R i6 : a+b o6 = a + b o6 : R

There are several functions that create rings for you. Generally, their variables are not globally visible. However, once you 'use' the ring, the variables are available.For example, the numerator of the Hilbert function is a polynomial in a ring with a variable T.

 i7 : T o7 = T o7 : Symbol i8 : hf = poincare ideal vars S 2 3 4 o8 = 1 - 4T + 6T - 4T + T o8 : ZZ[T] i9 : T o9 = T o9 : Symbol i10 : use ring hf o10 = ZZ[T] o10 : PolynomialRing i11 : T o11 = T o11 : Symbol

## Caveat

Any values stored in the variables that have been assigned to are lost, hence this operation should not be used by code in a package.