Are there any references on linear algebra (module theory) over non unital rings?












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Are there any references on linear algebra (module theory) over non unital rings? What are the main differences with unital rings in that respect?










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  • $begingroup$
    The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
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    – egreg
    Jan 15 at 23:20












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    Can you elaborate on this simple reason?
    $endgroup$
    – Patrick Sole
    Jan 15 at 23:26








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    @PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
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    – rschwieb
    Jan 16 at 0:47










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    Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
    $endgroup$
    – Jyrki Lahtonen
    Jan 17 at 22:54
















3












$begingroup$


Are there any references on linear algebra (module theory) over non unital rings? What are the main differences with unital rings in that respect?










share|cite|improve this question









$endgroup$












  • $begingroup$
    The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
    $endgroup$
    – egreg
    Jan 15 at 23:20












  • $begingroup$
    Can you elaborate on this simple reason?
    $endgroup$
    – Patrick Sole
    Jan 15 at 23:26








  • 1




    $begingroup$
    @PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
    $endgroup$
    – rschwieb
    Jan 16 at 0:47










  • $begingroup$
    Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
    $endgroup$
    – Jyrki Lahtonen
    Jan 17 at 22:54














3












3








3





$begingroup$


Are there any references on linear algebra (module theory) over non unital rings? What are the main differences with unital rings in that respect?










share|cite|improve this question









$endgroup$




Are there any references on linear algebra (module theory) over non unital rings? What are the main differences with unital rings in that respect?







ring-theory modules






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asked Jan 15 at 22:22









Patrick SolePatrick Sole

1177




1177












  • $begingroup$
    The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
    $endgroup$
    – egreg
    Jan 15 at 23:20












  • $begingroup$
    Can you elaborate on this simple reason?
    $endgroup$
    – Patrick Sole
    Jan 15 at 23:26








  • 1




    $begingroup$
    @PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
    $endgroup$
    – rschwieb
    Jan 16 at 0:47










  • $begingroup$
    Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
    $endgroup$
    – Jyrki Lahtonen
    Jan 17 at 22:54


















  • $begingroup$
    The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
    $endgroup$
    – egreg
    Jan 15 at 23:20












  • $begingroup$
    Can you elaborate on this simple reason?
    $endgroup$
    – Patrick Sole
    Jan 15 at 23:26








  • 1




    $begingroup$
    @PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
    $endgroup$
    – rschwieb
    Jan 16 at 0:47










  • $begingroup$
    Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
    $endgroup$
    – Jyrki Lahtonen
    Jan 17 at 22:54
















$begingroup$
The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
$endgroup$
– egreg
Jan 15 at 23:20






$begingroup$
The main difference is that almost nothing works. The reason is simple: defining $rx=0$ for every $rin R$ and every $xin A$ defines an $R$-module structure on the abelian group $A$. Something better happens when you require that $RA=A$, in order that $A$ is a module.
$endgroup$
– egreg
Jan 15 at 23:20














$begingroup$
Can you elaborate on this simple reason?
$endgroup$
– Patrick Sole
Jan 15 at 23:26






$begingroup$
Can you elaborate on this simple reason?
$endgroup$
– Patrick Sole
Jan 15 at 23:26






1




1




$begingroup$
@PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
$endgroup$
– rschwieb
Jan 16 at 0:47




$begingroup$
@PatrickSole doesn’t it seem a little bad that every Abelian group is a (nonunitary) module over every rng? That’s certainly not the case for unitary modules.
$endgroup$
– rschwieb
Jan 16 at 0:47












$begingroup$
Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
$endgroup$
– Jyrki Lahtonen
Jan 17 at 22:54




$begingroup$
Things break down severely. This is more or less the reason why I insist that rings should have multiplicative neutral elements :-)
$endgroup$
– Jyrki Lahtonen
Jan 17 at 22:54










1 Answer
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$begingroup$

Maybe not exactly what you're looking for, but these notes of Quillen say more about foundational matters regarding modules over non-unital rings than you probably thought possible!



He argues that the "correct" (I'm paraphrasing: he doesn't actually use that word) modules to consider are what he calls "firm modules".






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    $begingroup$

    Maybe not exactly what you're looking for, but these notes of Quillen say more about foundational matters regarding modules over non-unital rings than you probably thought possible!



    He argues that the "correct" (I'm paraphrasing: he doesn't actually use that word) modules to consider are what he calls "firm modules".






    share|cite|improve this answer









    $endgroup$


















      4












      $begingroup$

      Maybe not exactly what you're looking for, but these notes of Quillen say more about foundational matters regarding modules over non-unital rings than you probably thought possible!



      He argues that the "correct" (I'm paraphrasing: he doesn't actually use that word) modules to consider are what he calls "firm modules".






      share|cite|improve this answer









      $endgroup$
















        4












        4








        4





        $begingroup$

        Maybe not exactly what you're looking for, but these notes of Quillen say more about foundational matters regarding modules over non-unital rings than you probably thought possible!



        He argues that the "correct" (I'm paraphrasing: he doesn't actually use that word) modules to consider are what he calls "firm modules".






        share|cite|improve this answer









        $endgroup$



        Maybe not exactly what you're looking for, but these notes of Quillen say more about foundational matters regarding modules over non-unital rings than you probably thought possible!



        He argues that the "correct" (I'm paraphrasing: he doesn't actually use that word) modules to consider are what he calls "firm modules".







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 16 at 10:50









        Jeremy RickardJeremy Rickard

        17.1k11746




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