[ODE] matrix multiplication

[Henri Hakl]

That can't be quite right...

that would imply that you are multiplying a 3x4 with a 4x3 to get a 3x3
matrix.

Try
 dMultiply0(R, R, dBodyGetRotation(getBodyID()), 3, 3, 3);
or
 dMultiply0(R, R, dBodyGetRotation(getBodyID()), 4, 4, 4);
instead.

Though I can't guarantee what happens with those multiplication systems. If
you work with small matrices/vectors (3x1, 4x1, 3x3 and 4x4) I suggest you
download my geometry library at:

http://www.cs.sun.ac.za/~henri/aistuff.html#thetop

and look at the operations in there. The library contains highly optimized
geometry routines (such as matrix multiplication) for small vectors and
matrices. Admittedly the library is in Delphi, but the source is in
assembler and you can copy it over to C(++) with little effort.

----- Original Message -----
From: "Fig TaTam" <fig_tatam@hotmail.com>
To: <ode@q12.org>
Sent: Wednesday, March 12, 2003 11:25 PM
Subject: Re: [ODE] matrix multiplication


> I think I understand how to concatinate rotations, but it's not working.
Can
> you check if this code is right:
>
> dMatrix3 R;
> // then R is set to some rotation
> dMultiply0(R, R, dBodyGetRotation(getBodyID()), 3, 4, 3);
>
> So now R should equal to rotation of some dBody plus the rotation
originally
> held by R, is it right?
>
>
> >From: <jnilson_99@yahoo.com>
> >To: ode@q12.org
> >Subject: Re: [ODE] matrix multiplication
> >Date: Wed, 12 Mar 2003 08:27:41 -0800 (PST)
> >
> >
> >For what it's worth the following great book has a
> >simplified explanation of this and other matrix
> >tecniques. While not a "Game Math for Dummies" it does
> >explain matrix math simply and from a game programmer
> >point of view instead of the usual matrix explanations
> >which are geared toward mathematicians.
> >
>
>http://www.amazon.com/exec/obidos/tg/detail/-/1556229119/qid=1047486129/sr=
1-1/ref=sr_1_1/103-4731875-8322238?v=glance&s=books
> >
> >  So if you stupidly majored in something like History
> >realized Law School was a complete waste of time and
> >switched careers into game programming this book is
> >for you.
> >
> >john
> >
> >
> >
> >--- Henri Hakl <henri@cs.sun.ac.za> wrote:
> > > It's quite simple, consider:
> > >
> > > A = B * C
> > >
> > > if B is a 5 x 3 matrix and C is a 3 x 4 matrix then
> > > A will be a 5 x 4
> > > matrix, (B's second and C's first parameter HAVE to
> > > be the same, the
> > > resultant matrix has dimensions according to B's
> > > first and C's second
> > > parameter), accordingly you'd use:
> > >
> > > dMultiply0(A, B, C, 5, 3, 4)
> > >
> > >
> > > ----- Original Message -----
> > > From: "Fig TaTam" <fig_tatam@hotmail.com>
> > > To: <ODE@q12.org>
> > > Sent: Wednesday, March 12, 2003 12:32 PM
> > > Subject: [ODE] matrix multiplication
> > >
> > >
> > > > ok, I figured out how to do that rotation I
> > > wanted, so don't respond to
> > > > topic "Re: [ODE] rotation matrix from normalized
> > > vector?"
> > > >
> > > > But now I have a question about matrix
> > > multiplication. Ode has a function
> > > > for that described as:
> > > >
> > > > /* matrix multiplication. all matrices are stored
> > > in standard row format.
> > > > * the digit refers to the argument that is
> > > transposed:
> > > > *   0:   A = B  * C   (sizes: A:p*r B:p*q C:q*r)
> > > > *   1:   A = B' * C   (sizes: A:p*r B:q*p C:q*r)
> > > > *   2:   A = B  * C'  (sizes: A:p*r B:p*q C:r*q)
> > > > * case 1,2 are equivalent to saying that the
> > > operation is A=B*C but
> > > > * B or C are stored in standard column format.
> > > > */
> > > >
> > > > void dMultiply0 (dReal *A, const dReal *B, const
> > > dReal *C, int p,int q,int
> > > > r);
> > > >
> > > > What I don't understand is what I'm supposed to
> > > pass as 'p', 'q', and 'r'.
> > > > Anyone know?
> > > >
> > > >
> > >
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