Bug in tensor exp when arg has non-zero unit term

[inakleinbottle]

So I discovered a strange bug in the exp function when it is given a tensor with a non-zero unit element. I suspect the problem is in an optimisation of the multiplication logic but I will have to check. This only effects dense vectors, and presumably hybrid vectors when the dense part is sufficiently large.

dense_tensor_functions_float:26:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected 0 +/- 3e-08 but was 5.10864
dense_tensor_functions_double:26:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected 0 +/- 2e-15 but was 5.10864
dense_tensor_functions_rational:16:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected ...

[terrylyons]

Thank goodness for unit tests. This case needs care. It is tempting to use exp(c+l)=exp(c)exp(l). Since exp(c) is scalar one can use separate optimisations in its calculation. However, it is not required that scalar is commutative. I think we assume it is unital and a bi-module over the rationals. We also need that the tensor algebra is a left and a right module over the scalars. For example the scalars could ? be the truncated tensor algebra. The series for the exponential function in the tensor algebra has a very different flavour in the case where there is / is not a constant term. In the latter case it’s convergence is algebra. In the former case it is analysis. Log has similar issues. The involution as well. Does the bug already show when width = 1? Terry On 25 Aug 2021, at 18:29, inakleinbottle ***@***.***> wrote:  So I discovered a strange bug in the exp function when it is given a tensor with a non-zero unit element. I suspect the problem is in an optimisation of the multiplication logic but I will have to check. This only effects dense vectors, and presumably hybrid vectors when the dense part is sufficiently large. dense_tensor_functions_float:26:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected 0 +/- 3e-08 but was 5.10864 dense_tensor_functions_double:26:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected 0 +/- 2e-15 but was 5.10864 dense_tensor_functions_rational:16:1: error: Failure in tensor_exp_two_letters_plus_unit: Expected ... — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub<#27>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/ABQWN66POVGOTY5XSDASHZ3T6UK7TANCNFSM5CZQHIOA>. Triage notifications on the go with GitHub Mobile for iOS<https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android<https://play.google.com/store/apps/details?id=com.github.android&utm_campaign=notification-email>.