2
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Is there a way to make this work?

THM = TensorDimensions[M];
Assuming[ Element[M, Vectors[n]], 
    THM
]

Which gives:

TensorDimensions[M]

But I would like it to try executing the expression again, and get

{n}

None of these potential solutions work:

 Assuming[ Element[T, Vectors[n]],
      {THM, 
       Simplify[THM],
       Evaluate[THM]}
 ]  

This works, but is a profoundly ugly kludge:

 Assuming[ Element[T, Vectors[n]],
      {THM /. TensorDimensions[x_] :> TensorDimensions[x]}
 ]  

Can anyone explain what is happening here?

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1 Answer 1

2
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You need to use Update to tell Mathematica that hidden changes have been made that can affect results:

THM=TensorDimensions[M];
Assuming[Element[M,Vectors[n]],THM]

TensorDimensions[M]

Using Update:

Update[M];
Assuming[Element[M,Vectors[n]],THM]

{n}

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2
  • $\begingroup$ Thanks Carl. vv $\endgroup$ Feb 8, 2019 at 20:03
  • $\begingroup$ One question -- what else does Update[] do? Does it empty the cache of previous Simplify results? (And I realized Wolfram may change what it does whenever they want.) $\endgroup$ Feb 8, 2019 at 20:23

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