<p>The map from a free graded module onto all degree <var class="Arg">d</var> monomial generators of the finitely generated <strong class="pkg">homalg</strong> module <var class="Arg">M</var>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">m := MonomialMap( 1, M );</span>
<A homomorphism of graded left modules>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( m );</span>
x^2,0,0,
x*y,0,0,
x*z,0,0,
y^2,0,0,
y*z,0,0,
z^2,0,0,
0, x,0,
0, y,0,
0, z,0,
0, 0,1
the graded map is currently represented by the above 10 x 3 matrix
(degrees of generators of target: [ -1, 0, 1 ])
</pre></div>
<p>The resulting <strong class="pkg">homalg</strong> matrix consists of a generating set (over <span class="SimpleMath">R</span>) of the <var class="Arg">d</var>-th homogeneous part of the finitely generated <strong class="pkg">homalg</strong> <span class="SimpleMath">S</span>-module <var class="Arg">M</var>, where <span class="SimpleMath">R</span> is the coefficients ring of the graded ring <span class="SimpleMath">S</span> with <span class="SimpleMath">S_0=R</span>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">m := GeneratorsOfHomogeneousPart( 1, M );</span>
<An unevaluated non-zero 7 x 3 matrix over a graded ring>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( m );</span>
x^2,0,0,
x*y,0,0,
y^2,0,0,
0, x,0,
0, y,0,
0, z,0,
0, 0,1
(over a graded ring)
</pre></div>
<p>Compare with <code class="func">MonomialMap</code> (<a href="chap3.html#X7E7BA9887C435CD4"><span class="RefLink">3.6-1</span></a>).</p>
<p>The submodule of the <strong class="pkg">homalg</strong> module <var class="Arg">M</var> generated by the image of the <var class="Arg">d</var>-th monomial map (--> <code class="func">MonomialMap</code> (<a href="chap3.html#X7E7BA9887C435CD4"><span class="RefLink">3.6-1</span></a>)), or equivalently, by the generating set of the <var class="Arg">d</var>-th homogeneous part of <var class="Arg">M</var>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">n := SubmoduleGeneratedByHomogeneousPart( 1, M );</span>
<A graded left submodule given by 7 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( M );</span>
z, 0, 0,
0, y^2*z,z^2,
x^3,y^2, z
Cokernel of the map
Q[x,y,z]^(1x3) --> Q[x,y,z]^(1x3),
currently represented by the above matrix
(graded, degrees of generators: [ -1, 0, 1 ])
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( n );</span>
x^2,0,0,
x*y,0,0,
y^2,0,0,
0, x,0,
0, y,0,
0, z,0,
0, 0,1
A left submodule generated by the 7 rows of the above matrix
<p>The graded map induced by the homogeneous degree <em><span class="SimpleMath">1</span></em> ring element <var class="Arg">r</var> (of the underlying <strong class="pkg">homalg</strong> graded ring <span class="SimpleMath">S</span>) regarded as a <span class="SimpleMath">R</span>-linear map between the <var class="Arg">d</var>-th and the <span class="SimpleMath">(</span><var class="Arg">d</var><span class="SimpleMath">+1)</span>-st homogeneous part of the graded finitely generated <strong class="pkg">homalg</strong> <span class="SimpleMath">S</span>-module <span class="SimpleMath">M</span>, where <span class="SimpleMath">R</span> is the coefficients ring of the graded ring <span class="SimpleMath">S</span> with <span class="SimpleMath">S_0=R</span>. The generating set of both modules is given by <code class="func">GeneratorsOfHomogeneousPart</code> (<a href="chap3.html#X78127AB787A5C681"><span class="RefLink">3.6-3</span></a>). The entries of the matrix presenting the map lie in the coefficients ring <span class="SimpleMath">R</span>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">x := Indeterminate( S, 1 );</span>
x
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">m := RepresentationMapOfRingElement( x, M, 0 );</span>
<A "homomorphism" of graded left modules>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( m );</span>
1,0,0,0,0,0,0,
0,1,0,0,0,0,0,
0,0,0,1,0,0,0
the graded map is currently represented by the above 3 x 7 matrix
(degrees of generators of target: [ 1, 1, 1, 1, 1, 1, 1 ])
</pre></div>
<p>It is assumed that all indeterminates of the underlying <strong class="pkg">homalg</strong> graded ring <span class="SimpleMath">S</span> are of degree <span class="SimpleMath">1</span>. The output is the <strong class="pkg">homalg</strong> matrix of the multiplication map <span class="SimpleMath">Hom( A, M_<var class="Arg">d</var> ) -> Hom( A, M_<var class="Arg">d</var>+1 )</span>, where <span class="SimpleMath">A</span> is the Koszul dual ring of <span class="SimpleMath">S</span>, defined using the operation <code class="code">KoszulDualRing</code>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">A := KoszulDualRing( S, "a,b,c" );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">m := RepresentationMatrixOfKoszulId( 0, M );</span>
<An unevaluated 3 x 7 matrix over a graded ring>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( m );</span>
a,b,0,0,0,0,0,
0,a,b,0,0,0,0,
0,0,0,a,b,c,0
(over a graded ring)
</pre></div>
<p>It is assumed that all indeterminates of the underlying <strong class="pkg">homalg</strong> graded ring <span class="SimpleMath">S</span> are of degree <span class="SimpleMath">1</span>. The output is the the multiplication map <span class="SimpleMath">Hom( A, M_<var class="Arg">d</var> ) -> Hom( A, M_<var class="Arg">d</var>+1 )</span>, where <span class="SimpleMath">A</span> is the Koszul dual ring of <span class="SimpleMath">S</span>, defined using the operation <code class="code">KoszulDualRing</code>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">A := KoszulDualRing( S, "a,b,c" );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ] );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">m := RepresentationMapOfKoszulId( 0, M );</span>
<A homomorphism of graded left modules>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( m );</span>
a,b,0,0,0,0,0,
0,a,b,0,0,0,0,
0,0,0,a,b,c,0
the graded map is currently represented by the above 3 x 7 matrix
(degrees of generators of target: [ 4, 4, 4, 4, 4, 4, 4 ])
</pre></div>
<p>It is assumed that all indeterminates of the underlying <strong class="pkg">homalg</strong> graded ring <span class="SimpleMath">S</span> are of degree <span class="SimpleMath">1</span>. Compute the <strong class="pkg">homalg</strong> <span class="SimpleMath">A</span>-cocomplex <span class="SimpleMath">C</span> of Koszul maps of the <strong class="pkg">homalg</strong> <span class="SimpleMath">S</span>-module <var class="Arg">M</var> (--> <code class="func">RepresentationMapOfKoszulId</code> (<a href="chap3.html#X7DBC9F4F827B4F01"><span class="RefLink">3.6-7</span></a>)) in the <span class="SimpleMath">[</span> <var class="Arg">degree_lowest</var> .. <var class="Arg">degree_highest</var> <span class="SimpleMath">]</span>. The Castelnuovo-Mumford regularity of <var class="Arg">M</var> is characterized as the highest degree <span class="SimpleMath">d</span>, such that <span class="SimpleMath">C</span> is not exact at <span class="SimpleMath">d</span>. <span class="SimpleMath">A</span> is the Koszul dual ring of <span class="SimpleMath">S</span>, defined using the operation <code class="code">KoszulDualRing</code>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">A := KoszulDualRing( S, "a,b,c" );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x^3, y^2, z, z, 0, 0 ]", 2, 3, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := LeftPresentationWithDegrees( M, [ -1, 0, 1 ], S );</span>
<A graded non-torsion left module presented by 2 relations for 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">CastelnuovoMumfordRegularity( M );</span>
1
<span class="GAPprompt">gap></span> <span class="GAPinput">R := KoszulRightAdjoint( M, -5, 5 );</span>
<A cocomplex containing 10 morphisms of graded left modules at degrees
[ -5 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := KoszulRightAdjoint( M, 1, 5 );</span>
<An acyclic cocomplex containing
4 morphisms of graded left modules at degrees [ 1 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := KoszulRightAdjoint( M, 0, 5 );</span>
<A cocomplex containing 5 morphisms of graded left modules at degrees
[ 0 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := KoszulRightAdjoint( M, -5, 5 );</span>
<A cocomplex containing 10 morphisms of graded left modules at degrees
[ -5 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">H := Cohomology( R );</span>
<A graded cohomology object consisting of 11 graded left modules at degrees
[ -5 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">ByASmallerPresentation( H );</span>
<A non-zero graded cohomology object consisting of
11 graded left modules at degrees [ -5 .. 5 ]>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, -2 );</span>
<A graded zero left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, -3 );</span>
<A graded zero left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, -1 );</span>
<A graded cyclic torsion-free non-free left module presented by 2 relations fo\
r a cyclic generator>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, 0 );</span>
<A graded non-zero cyclic left module presented by 3 relations for a cyclic ge\
nerator>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, 1 );</span>
<A graded non-zero cyclic left module presented by 2 relations for a cyclic ge\
nerator>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, 2 );</span>
<A graded zero left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, 3 );</span>
<A graded zero left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Cohomology( R, 4 );</span>
<A graded zero left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( Cohomology( R, -1 ) );</span>
Q{a,b,c}/< b, a >
(graded, degree of generator: 0)
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( Cohomology( R, 0 ) );</span>
Q{a,b,c}/< c, b, a >
(graded, degree of generator: 0)
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( Cohomology( R, 1 ) );</span>
Q{a,b,c}/< b, a >
<p>The degree <span class="SimpleMath">d</span> homogeneous part of the graded <span class="SimpleMath">R</span>-module <var class="Arg">M</var> as a module over the coefficient ring or field of <span class="SimpleMath">R</span>.</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">R := HomalgFieldOfRationalsInDefaultCAS( ) * "x,y,z";;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">S := GradedRing( R );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := HomalgMatrix( "[ x, y^2, z^3 ]", 3, 1, S );;</span>
<span class="GAPprompt">gap></span> <span class="GAPinput">M := Subobject( M, ( 1 * S )^0 );</span>
<A graded torsion-free (left) ideal given by 3 generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">CastelnuovoMumfordRegularity( M );</span>
4
<span class="GAPprompt">gap></span> <span class="GAPinput">M1 := HomogeneousPartOverCoefficientsRing( 1, M );</span>
<A graded left vector space of dimension 1 on a free generator>
<span class="GAPprompt">gap></span> <span class="GAPinput">gen1 := GeneratorsOfModule( M1 );</span>
<A set consisting of a single generator of a homalg left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( M1 );</span>
Q^(1 x 1)
(graded, degree of generator: 1)
<span class="GAPprompt">gap></span> <span class="GAPinput">M2 := HomogeneousPartOverCoefficientsRing( 2, M );</span>
<A graded left vector space of dimension 4 on free generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( M2 );</span>
Q^(1 x 4)
(graded, degrees of generators: [ 2, 2, 2, 2 ])
<span class="GAPprompt">gap></span> <span class="GAPinput">gen2 := GeneratorsOfModule( M2 );</span>
<A set of 4 generators of a homalg left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">M3 := HomogeneousPartOverCoefficientsRing( 3, M );</span>
<A graded left vector space of dimension 9 on free generators>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( M3 );</span>
Q^(1 x 9)
(graded, degrees of generators: [ 3, 3, 3, 3, 3, 3, 3, 3, 3 ])
<span class="GAPprompt">gap></span> <span class="GAPinput">gen3 := GeneratorsOfModule( M3 );</span>
<A set of 9 generators of a homalg left module>
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( gen1 );</span>
x
a set consisting of a single generator given by (the row of) the above matrix
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( gen2 );</span>
x^2,
x*y,
x*z,
y^2
a set of 4 generators given by the rows of the above matrix
<span class="GAPprompt">gap></span> <span class="GAPinput">Display( gen3 );</span>
x^3,
x^2*y,
x^2*z,
x*y*z,
x*z^2,
x*y^2,
y^3,
y^2*z,
z^3
a set of 9 generators given by the rows of the above matrix
</pre></div>
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