Mathematica and cross products...

[homercles337]

I have never used Mathematica before. It looks like it will do n-dimensional cross products, but im on a cripled version of Mathematica (called reader or something). We have a license, but the IT folks are 8-5ers. Is it possible to see the functions in Mathematica (ie Matlab)? If so how? Thanks.

BTW, i have already written the 3d cross so that is not useful.

 

[cleverhandle]

Originally posted by: homercles337
It looks like it will do n-dimensional cross products...

It will certainly do that.

but im on a cripled version of Mathematica (called reader or something).

Right, reader just lets you view existing notebooks, not create your own calculations.

Is it possible to see the functions in Mathematica

A searchable function index is here

(ie Matlab)

Mathematica != Matlab if that's what you're implying. Completely different products.

 

[homercles337]

Yes, im aware that mathematica is not matlab (been using matlab for 9 years, and my coadvisor in grad school kept trying to get me to use mathematica). In matlab if you type "edit cross" you can see the function that is called. The only functions you cant see are those that are compiled (mex/core/p). If you know of source for n-d cross product anywhere that is all im really looking for. Even a paper would be useful. Im turning up a great big fat zero, or papers on 3-d and 7-d. Im not a math weenie, im just looking to implement n-d cross products in matlab/C++. I could do it myself, but theres no sense reinventing the wheel...plus it would take more time than i want.

 

[cleverhandle]

Ah... I see what you're after, now - it wasn't clear from the OP. And unfortunately, I don't know enough about Mathematica to be able to help you - I no longer have a copy around to play with, sadly. Hopefully someone else will swing by eventually...

 

[WildHorse]

I have Mathematica 5.2.

Has a steep learning curve, but is incredibley powerful.

I'm not that clear about what you need, but wonder if these might be helpful to you?
http://documents.wolfram.com/teachersedition/RefGuide/Cross.html

http://search.wolfram.com/index.en.cgi?restrict=Main&q=cross+product

http://documents.wolfram.com/mathematica/book/section-1.8.3

http://search.wolfram.com/index.en.cgi?restrict=Main&q=cross+product

 

[cleverhandle]

Originally posted by: scott
I'm not that clear about what you need, but wonder if these might be helpful to you?

What he wants to do is basically decompile the higher-level Mathematica commands into lower level elements that could be used in a C++ program or matlab. I don't know enough to say whether that sort of thing is possible.

 

[WildHorse]

Originally posted by: cleverhandle

Originally posted by: scott
I'm not that clear about what you need, but wonder if these might be helpful to you?

What he wants to do is basically decompile the higher-level Mathematica commands into lower level elements that could be used in a C++ program or matlab. I don't know enough to say whether that sort of thing is possible.

Doubt I'm advanced enough with it to be of help with something like that.

I hope he's able to get some benefit from the links you & I gave him. Maybe he can figure it out from what they explain.

 

[CP5670]

heh, I'm in the opposite situation. I use Mathematica on a daily basis but have to write a Matlab program for a class, so I'm trying to pick up Matlab quickly this weekend. 😛 Anyone know if there is a built-in function for finding the hessian of a function at a point?

Unfortunately, Mathematica doesn't let you see most of the built in functions, which are all compiled (unless they come in separate packages, which the Cross one doesn't). I don't know much about the cross product in higher dimensions, but the type that Mathematica's Cross function does is apparently just a determinant calculation (the thing given here). I have no idea about the 7D binary product though.

 

[homercles337]

Thanks for the links, but they are not useful. I want to see the actual algebra that went into calcuating the cross not just the output. In matlab this does the 3d cross:

c = [a(2,:).*b(3,:)-a(3,:).*b(2,:)
     a(3,:).*b(1,:)-a(1,:).*b(3,:)
     a(1,:).*b(2,:)-a(2,:).*b(1,:)];

a and b are the input 3-vectors. But it looks like (according to cp5670, thanks) that you cant look at this suff in mathematica. D'oh! Any textbook/paper recommendations that cover n-d cross products? All my sources only do 3 dimensions.

PSA, a steep learning curve means that you learn a lot in a short time and a shallow one means that it takes a long time to learn. This is a VERY common misconception.