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# expression(ToricDivisor) -- get the expression used to format for printing

- Function: expression
- Usage:
    `expression D`
- Inputs:
  - D, a toric divisor,
- Outputs:
  - an expression, used to format D for printing

## Description

This method is the primary function called upon by << to format for printing. It assumes that D is well-defined.

When the underlying normal toric variety has not been assigned a global variable, the $i$-th irreducible torus-invariant Weil divisor is displayed as $D_i$. However, if the underlying normal toric variety has been assigned a global variable $X$, the $i$-th irreducible torus-invariant Weil divisor is displayed as $X_i$. In either case, an arbitrary torus-invariant Weil divisor is displayed as an integral linear combination of these expressions.

    i1 : toricDivisor({2,-7,3}, toricProjectiveSpace 2)

    o1 = 2*D  - 7*D  + 3*D
            0      1      2

    o1 : ToricDivisor on normalToricVariety ({{-1, -1}, {1, 0}, {0, 1}}, {{0, 1}, {0, 2}, {1, 2}})

    i2 : toricDivisor convexHull (id_(ZZ^3) | - id_(ZZ^3))

    o2 = D  + D  + D  + D  + D  + D  + D  + D
          0    1    2    3    4    5    6    7

    o2 : ToricDivisor on normalToricVariety ({{1, 1, 1}, {-1, 1, 1}, {1, -1, 1}, {-1, -1, 1}, {1, 1, -1}, {-1, 1, -1}, {1, -1, -1}, {-1, -1, -1}}, {{0, 1, 2, 3}, {0, 1, 4, 5}, {0, 2, 4, 6}, {1, 3, 5, 7}, {2, 3, 6, 7}, {4, 5, 6, 7}})

    i3 : PP2 = toricProjectiveSpace 2;

    i4 : D1 = toricDivisor({2,-7,3}, PP2)

    o4 = 2*PP2  - 7*PP2  + 3*PP2
              0        1        2

    o4 : ToricDivisor on PP2

    i5 : D2 = 2 * PP2_0 - 7 * PP2_1 + 3 * PP2_2

    o5 = 2*PP2  - 7*PP2  + 3*PP2
              0        1        2

    o5 : ToricDivisor on PP2

    i6 : assert(D1 == D1)

## See also

- working with divisors -- information about toric divisors and their related groups
- isWellDefined(ToricDivisor) -- whether a toric divisor is well-defined
- NormalToricVariety _ ZZ -- make an irreducible torus-invariant divisor

## Ways to use this method:

- expression(ToricDivisor) -- get the expression used to format for printing

The source of this document is in /build/macaulay2-88fgJW/macaulay2-1.25.11+ds/M2/Macaulay2/packages/NormalToricVarieties/DivisorsDocumentation.m2:771:0.