6086 6087 nan to indicate no_channel, split dim singleton

[wyli]

Description

Fixes #6086 remove the channel check
Fixes #6087 internally using float('nan') to also represent "no_channel"

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[wyli]

/build

[Nic-Ma]

Hi @wyli ,

Could you please help explain more about the use case to collate a "no-channel" Tensor and a "channel-first" Tensor?

Thanks in advance.

[wyli]

Both issues are from dealing with a dataset that has both no-channel gray-scale images and 3-channel RGB images in PNG files

[wyli]

/build