[Numpy-discussion] performance matrix multiplication vs. matlab

Benoit Jacob jacob.benoit.1@gmail....
Mon Jan 18 10:26:01 CST 2010


2010/1/18 Robert Kern <robert.kern@gmail.com>:
> On Mon, Jan 18, 2010 at 09:35, Benoit Jacob <jacob.benoit.1@gmail.com> wrote:
>
>> Sorry for continuing the licensing noise on your list --- I though
>> that now that I've started, I should let you know that I think I
>> understand things more clearly now ;)
>
> No worries.
>
>> First, Section 5 of the LGPL is horrible indeed, so let's forget about that.
>
> I don't think it's that horrible, honestly. It just applies to a
> different deployment use case and a different set of technologies.
>
>> If you were using a LGPL-licensed binary library, Section 4 would
>> rather be what you want. It would require you to:
>>  4a) say somewhere ("prominently" is vague, the bottom of a README is
>> OK) that you use the library
>>  4b) distribute copies of the GPL and LGPL licenses text. Pointless,
>> but not a big issue.
>>
>> the rest doesn't matter:
>>  4c) not applicable to you
>>  4d1) this is what you would be doing anyway
>
> Possibly, but shared libraries are not easy for a variety of boring,
> Python-specific, technical reasons.

Ah, that I didn't know.

>>  4e) not applicable to you
>
> Yes, it is. The exception where Installation Information is not
> required is only when installation is impossible, such as embedded
> devices where the code is in a ROM chip.

OK, I didn't understand that.

>
>> Finally and this is the important point: you would not be passing any
>> requirement to your own users. Indeed, the LGPL license, contrary to
>> the GPL license, does not propagate through dependency chains. So if
>> NumPy used a LGPL-licensed lib Foo, the conditions of the LGPL must be
>> met when distributing NumPy, but NumPy itself isn't LGPL at all and an
>> application using NumPy does not have to care at all about the LGPL.
>> So there should be no concern at all of "passing on LGPL requirements
>> to users"
>
> No, not at all. The GPL "propagates" by requiring that the rest of the
> code be licensed compatibly with the GPL. This is an unusual and
> particular feature of the GPL. The LGPL does not require that rest of
> the code be licensed in a particular way. However, that doesn't mean
> that the license of the "outer layer" insulates the downstream user
> from the LGPL license of the wrapped component. It just means that
> there is BSD code and LGPL code in the total product. The downstream
> user must accept and deal with the licenses of *all* of the components
> simultaneously. This is how most licenses work. I think that the fact
> that the GPL is particularly "viral" may be obscuring the normal way
> that licenses work when combined with other licenses.
>
> If I had a proprietary application that used an LGPL library, and I
> gave my customers some limited rights to modify and resell my
> application, they would still be bound by the LGPL with respect to the
> library. They could not modify the LGPLed library and sell it under a
> proprietary license even if I allow them to do that with the
> application as a whole. For us to use Eigen2 in numpy such that our
> users could use, modify and redistribute numpy+Eigen2, in its
> entirety, under the terms of the BSD license, we would have to get
> permission from you to distribute Eigen2 under the BSD license. It's
> only polite.

OK, so the Eigen code inside of NumPy would still be protected by the
LGPL. But what I meant when I said that the LGPL requirements don't
propagate to your users, was that, for example, they don't have to
distribute copies of the LGPL text, installation information for
Eigen, or links to Eigen's website.

The only requirement, if I understand well, is that _if_ a NumPy user
wanted to make modifications to  Eigen itself, he would have to
conform to the LGPL requirements about sharing the modified source
code.

But is it really a requirement of NumPy that all its dependencies must
be free to modify without redistributing the modified source code?
Don't you use MKL, for which the source code is not available at all?
I am not sure that I understand how that is better than having source
code subject to LGPL requirements.

Benoit


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