Is there a big performance difference between python's sum and ortools' solver.Sum?

[Li Mike]

Whien building constraints in a lp model, both python's sum and  solver.Sum work.

Which one is better?

If the  performance difference is not big, I would like to use sum.

Any suggestion?

[blind.line]

I think the python sum won’t do the right thing. You should use solver.Sum

See the code here: https://github.com/google/or-tools/blob/b77bd3ac69b7f3bb02f55b7bab6cbb4bab3917f2/ortools/constraint_solver/python/constraint_solver.i#L764. 

Renames MakeSum to Sum, but it accepts a list of IntVar and does the right thing with them. Don’t be fooled by the similar naming. 

James

On Mar 3, 2021, at 19:20, Li Mike <qtb...@gmail.com> wrote:

Whien building constraints in a lp model, both python's sum and  solver.Sum work.

Which one is better?

If the  performance difference is not big, I would like to use sum.

Any suggestion?

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[blind.line]

Oh ... caveat to my posted reply. I just noticed you were asking about LP model. I’ve only used routing solver and CP-SAT solvers. It might be different for LP, but I’d guess not. 

James

On Mar 3, 2021, at 19:20, Li Mike <qtb...@gmail.com> wrote:

Whien building constraints in a lp model, both python's sum and  solver.Sum work.

Which one is better?

If the  performance difference is not big, I would like to use sum.

Any suggestion?

--

[Laurent Perron]

The sum() creates a very unbalanced syntax tree. The traversal of this tree can be expensive for large expressions (above a few thousands terms). 

Solver.Sum() creates one flat expression which can be significantly faster for these large expressions. 

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[Priidik Vilumaa]

So we should always use solver.Sum()? Does this hold for all solvers (where applicable)?

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[Laurent Perron]

In python, 

use solver.Sum() for the routing solver and the linear solver.

The API is cp_model.LinearExpr.Sum() for CP-SAT.

It depends, if you know the size is small, use sum(). If the size is data dependent, use Sum().

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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