RegularChains[ConstructibleSetTools]
MakePairwiseDisjoint
make the defining regular systems in a constructible set pairwise disjoint
Calling Sequence
Parameters
Description
Examples
MakePairwiseDisjoint(cs, R)
cs
-
constructible set
R
polynomial ring
The command MakePairwiseDisjoint(cs, R) returns a constructible set cs1 such that cs1 and cs are equal and the regular systems representing cs1 are pairwise disjoint.
Generally, in a constructible set, there is some redundancy among its components defined by regular systems. By default, functions on constructible sets do not remove redundancy because such a computation is expensive.
This command is part of the RegularChains[ConstructibleSetTools] package, so it can be used in the form MakePairwiseDisjoint(..) only after executing the command with(RegularChains[ConstructibleSetTools]). However, it can always be accessed through the long form of the command by using RegularChains[ConstructibleSetTools][MakePairwiseDisjoint](..).
with⁡RegularChains:
with⁡ConstructibleSetTools:
First, define the polynomial ring.
R≔PolynomialRing⁡x,y,a,b,c,d,e
R≔polynomial_ring
Consider the following almost general linear equations. They are not completely general, since their constant term, namely e, is the same.
F≔a⁢x+b⁢y−e
G≔c⁢x+d⁢y−e
After projecting the variety defined by F and G into the parameter space given by the last 5 variables, you can see when such general linear equations have solutions after specializing the last 5 variables.
cs≔Projection⁡F,G,5,R
cs≔constructible_set
lrs≔RepresentingRegularSystems⁡cs,R
lrs≔regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system
Info⁡cs,R
,c,d⁢a−b⁢c,a−c,b−d,c,c,d,a,d⁢a−b⁢c,e,d,c,a,b−d,c,d,a,c,e,1,b,d,e,1,c,d,e,a,a,b,c,d,e,1
nops⁡lrs
9
There are 9 regular systems defining the image cs of the projection. To remove common parts of these regular systems, use MakePairwiseDisjoint.
cs_mpd≔MakePairwiseDisjoint⁡cs,R
cs_mpd≔constructible_set
lcs_mpd≔RepresentingRegularSystems⁡cs_mpd,R
lcs_mpd≔regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system,regular_system
nops⁡lcs_mpd
Now, there are 10 components.
Info⁡cs_mpd,R
a,b,c,d,e,1,c,d,e,a,b,b,d,e,a−c,a,c,e,b−d,d⁢a−b⁢c,e,d,c,b−d,a,b−d,c,d,c,d,a,a−c,b−d,c,,c,d⁢a−b⁢c
Notice that some components have split during the redundancy removal.
See Also
ConstructibleSet
ConstructibleSetTools
GeneralConstruct
Projection
RefiningPartition
RegularChains
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