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ExteriorModules :: isStableModule

isStableModule -- whether a monomial module over an exterior algebra is stable

Synopsis

Description

Let $\{g_1,g_2,\ldots,g_r\}$ be a graded basis of F with $deg(g_i)=f_i,\ i=1,\ldots,r.$ A monomial submodule $M=\oplus_{i=1}^{r}{I_ig_i}$ of F is stable if it is almost stable and $(x_1,\ldots,x_n)^{(f_{i+1}-f_i)} I_{i+1}$ belongs to $I_i$ for $i=1,\ldots,r-1.$ A monomial ideal $I$ of $E$ is called stable if for each monomial $e_{\sigma}\in I$ and each $j < \mathrm{m}(e_{\sigma})$ one has $e_j e_{{\sigma} \setminus \{\mathrm{m}(e_{\sigma})\}} \in I.$

Example:

i1 : E = QQ[e_1..e_4, SkewCommutative => true]

o1 = E

o1 : PolynomialRing, 4 skew commutative variables
 
i2 : F=E^{0,0}

      2
o2 = E

o2 : E-module, free
 
i3 : I_1=ideal(e_1*e_2)

o3 = ideal(e e )
            1 2

o3 : Ideal of E
 
i4 : I_2=ideal(e_1*e_2*e_3,e_1*e_2*e_4,e_1*e_3*e_4)           

o4 = ideal (e e e , e e e , e e e )
             1 2 3   1 2 4   1 3 4

o4 : Ideal of E
 
i5 : M=createModule({I_1,I_2},F)

o5 = image | e_1e_2 0         0         0         |
           | 0      e_1e_3e_4 e_1e_2e_4 e_1e_2e_3 |

                             2
o5 : E-module, submodule of E
 
i6 : isAlmostStableModule M

o6 = true
 
i7 : isStableModule M

o7 = false

See also

Ways to use isStableModule :

For the programmer

The object isStableModule is a method function.