[ODE] need to understand this

[pia dalusong]

hello,

after a lot of digging, i saw this
void dRFromEulerAngles (dMatrix3 R, dReal phi, dReal
theta, dReal psi)
{
  dReal sphi,cphi,stheta,ctheta,spsi,cpsi;
  dAASSERT (R);
  sphi = dSin(phi);
  cphi = dCos(phi);
  stheta = dSin(theta);
  ctheta = dCos(theta);
  spsi = dSin(psi);
  cpsi = dCos(psi);
  _R(0,0) = cpsi*ctheta;
  _R(0,1) = spsi*ctheta;
  _R(0,2) =-stheta;
  _R(1,0) = cpsi*stheta*sphi - spsi*cphi;
  _R(1,1) = spsi*stheta*sphi + cpsi*cphi;
  _R(1,2) = ctheta*sphi;
  _R(2,0) = cpsi*stheta*cphi + spsi*sphi;
  _R(2,1) = spsi*stheta*cphi - cpsi*sphi;
  _R(2,2) = ctheta*cphi;
}
i'm a little confused as to how you put values into a
dMatrix and how do you call it?
if i have a variable 
const dReal *R
and 
dMatrix3 M

is R[0]=m[0,0] ?
i'm sorry but i don't understand what happens when you
write _R(2,1)

is it an 2d array matrix[3][3] or a 1d matrix[12]?

thanks



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