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evalf / nutils

The nutils project
http://www.nutils.org/
MIT License
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Variable arguments for Add and Multiply #788

Closed gertjanvanzwieten closed 1 year ago

gertjanvanzwieten commented 1 year ago

This PR changes the Multiply and Add operations to support any number of arguments for faster evaluation and more efficient simplifications.

For operations organized in a tree such as (A + B) + (C + D) it is difficult to discover relevant structures, for instance A and D having matching sparsity. In the current form, the only way to properly discover this is if (A + B)._add(C + D) dispatches to A._add(C + D) as well as the reverse (C + D)._add(A), and from there to D._add(A). While fuctional, it is impossible to avoid redundancy (C + D)._add(A + B) will explore most of the same combinations - a problem that grows rapidly with the depth of the tree. By moving to a flat structure A + B + C + D it is trivial to find patterns with minimal effort. Moreover, most simplifications currently defined on Add and Multiply are already valid for multiple arguments, so the new structure does not add complexity.

gertjanvanzwieten commented 1 year ago

Closing in favour of #818