Hi,

On Sun, Sep 1, 2013 at 12:38 PM, Gilbert Gede <[email protected]> wrote:
> Check out this PR for a discussion of appropriateness of dummification:
> https://github.com/sympy/sympy/pull/1920
>
> Here's the new PR with the correction:
> https://github.com/sympy/sympy/pull/2428

If I understand correctly, you are trying to guess whether the person
calling lambdify wants numerical implementations or not.

I agree with your comment on the PR: "But I see your point about
symbols/expressions vs. sub_/big_expressions. But I would think with
lambdify, as it is intended for preparing for numerical evaluation,
that this wouldn't be a concern." :
https://github.com/sympy/sympy/pull/1920

At the moment you try to guess based on whether someone explicitly
passed 'sympy' as the modules argument, or the first argument to
modules (it's not the default).

For example, it might be the case that someone passed 'sympy' as the
first argument, but 'numpy' as the second, and all the functions in
the expression are numpy functions.  Or the user  might pass 'sympy'
as the modules, and have an implemented function in the expression, so
clearly does want numerical implementation.

So it seems to me the problem here is that you are having to use an
implicit heuristic to determine what the function does, and it would
be hard to guess how to change the behavior of the function without
reading to the code to work out the heuristic.

I think Jason is right - 'dummify' should be an argument to lambdify;
if you really want the heuristic, it should be in the case where
'dummify' is None.

Cheers,

Matthew

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