1525 add MultiScaleLoss

[kate-sann5100]

Signed-off-by: kate-sann5100 yiwen.li@st-annes.ox.ac.uk

Fixes #1525.

Description

Add MultiScaleLoss

Status

Ready/Work in progress/Hold

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 --codeformat --coverage.
• Quick tests passed locally by running ./runtests.sh --quick.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[wyli]

thanks! please see a few comments inline

[wyli]

thanks!