## Changing the Type of a Module in MAGMA

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I am currently working with irreducible $k[G]$-modules in MAGMA for finite fields $k$ and finite groups $G$. To construct these modules, I am using the commands IrreducibleModules(G,k) This results in MAGMA recognising the modules as being of type $ModGrp$. However, I wish to perform calculations such as finding the projective cover of such a module, for which MAGMA can only perform such calculations on modules over algebras (i.e. of type $ModAlg$). Is there an easy way to coerce MAGMA into treating modules of type $ModGrp$ as being of type $ModAlg$?

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## 1 Answer

MAGMA is perfectly capable of calculating the projective cover of a member of `IrreducibleModules(G,k)`, via the `ProjectiveCover()` function. You can also just call `ProjectiveIndecomposables(G,k)`. Perhaps you are running an old version of MAGMA? Version 2.18-3 is certainly capable of this functionality.

(This would have been a comment rather than an answer if reputation allowed).

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Thanks for the comment. I have tried using these commands, but just get the error messages: Runtime error in 'ProjectiveCover': Bad argument types Argument types given: ModGrp. Perhaps it is as you suggested that the version of MAGMA that I am using is too old (it is V2.15-15) – dward1996 Apr 18 2012 at 14:47

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I believe the projective modules functionality was introduced in V2.17, so you will need to update. – Alastair Litterick Apr 18 2012 at 15:20
@AlistariLitterick Thanks for clarifying that. – dward1996 Apr 18 2012 at 15:22
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