PyWSTP

Szabolcs

10:14

I am not fluent in low-level MathLink and I have to experiment and read docs every time before doing something like this.

However, my impression was that transferring an array through a link does not unpack it.

If a given thing is put on a link, there are usually multiple ways to retrieve it. E.g. if you put an integer, you get still get a string (a string representation of the integer).

I'd assume that if you put a Real packed array, the optimal way to get it would be MLGetReal64Array

I don't have the time to test these things right now.

Why do you think the kernel unpacks?

Kh40tiK

I'm not sure. But WSGetType do not give WSTKPACKED or alike

Szabolcs

What I'm trying to say is that even if you send a packed array, you could retrieve it as a "Funtcion" with head "List", then get numbers one by one. That's effective unpacking.

The efficient way to get it would be WSGetReal64List or WSGetReal64Array

What does it give then? MLTKARRAY?

Kh40tiK

No, just MLTKFUNC, then MLTKREAL

everything the client side sees are just MKTL{FUNC,INT,REAL,SYM,STR}

Szabolcs

I'd have to experiment with this, and unfortunately I wouldn't really have the time until the weekend

Kh40tiK

Thank you for your time

Szabolcs

10:19

But it sound like a very exciting and useful project to do this for Python

and a potential basis for a good Python link

not like the ExternalEvaluate stuff but much better

Kh40tiK

It's still in very early stage of dev, I would be open to design suggestions.

Szabolcs

10:31

@Kh40tiK So basically you just want to detect if it's possible to use MLGetReal64Array or MLGetInteger64Array to get the next thing on the link, for performance reasons.

I confirm your finding with MLGetType

Kh40tiK

Yup. Iteratively filling a multidim array in python could be horribly slow.

Szabolcs

Have you investigated MLGetRawType?

Kh40tiK

Hum, didn't know this one.

Szabolcs

If you work with MathLink, don't rely on the documentation

It's incomplete and on occasion incorrect

You need to look at the header file and experiment

I also didn't know MLGetRawType, I just found it in the header right next to MLGetType

Kh40tiK

Okay I see. Thanks.

I'll update later.

Szabolcs

10:35

Now I'm getting an A for a packed integer array

that's ...

#define MLTKARRAY 'A' /* 65 0x41 01000001 */

I guess you did look at the header, otherwise you wouldn't have found MLTKPACKED. right?

Is it documented anywhere?

So now we know it's an array, but we don't know its dimension and type (Integer or Real)

It also says, /* The following defines are for internal use only */, for these codes ...

Kh40tiK

WSGetArrayType maybe this one?

Szabolcs

let me try

what's an array_meterp meterp?

Kh40tiK

dunno, could be a "dtype" or "shape" thing as in numpy

opaque struct

Szabolcs

First: is that argument an input or an output of that function? If an input, how do we get it? Is there another function for that?

It looks very much like an input

Kh40tiK

this link looks helpful

Szabolcs

10:44

That would suggest that any function that outputs it must take a pointer to an array_meterp, i.e. an array_meterpp (note the two Ps)

There are only a few such function, but they're even more cryptic

Kh40tiK

development turns into hacking :P

Szabolcs

That's a very old thread, and MLGetArrayType0 seems deprecated

it's replaced with MLGetArrayTypeWithDepthAndLeafType

BUT the post you found explains what the "heads link" is, so progress!

I really can't spend more time on it today, but please keep posting your findings in this room

Kh40tiK

I'll keep updating

Bye

Szabolcs

Make sure you look at the #if MLINTERFACE >= 4 parts of the header. The rest will not work with interface 4. It's useful to use an IDE that understands some of the code to browse the header. E.g. I see this:

Makes it much easier to browse the code and ignore parts belonging to earlier APIs

I use Qt Creator, but there are many other tools that can do this

Chatroom for this question: mathematica.stackexchange.com/questions/180706/…

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Bye

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