ardupilot/Arducopter/Vector.pde

//Computes the dot product of two vectors
float Vector_Dot_Product(float vector1[3],float vector2[3])
{
  float op=0;
  
  for(int c=0; c<3; c++)
  {
  op+=vector1[c]*vector2[c];
  }
  
  return op; 
}

//Computes the cross product of two vectors
void Vector_Cross_Product(float vectorOut[3], float v1[3],float v2[3])
{
  vectorOut[0]= (v1[1]*v2[2]) - (v1[2]*v2[1]);
  vectorOut[1]= (v1[2]*v2[0]) - (v1[0]*v2[2]);
  vectorOut[2]= (v1[0]*v2[1]) - (v1[1]*v2[0]);
}

//Multiply the vector by a scalar. 
void Vector_Scale(float vectorOut[3],float vectorIn[3], float scale2)
{
  for(int c=0; c<3; c++)
  {
   vectorOut[c]=vectorIn[c]*scale2; 
  }
}

void Vector_Add(float vectorOut[3],float vectorIn1[3], float vectorIn2[3])
{
  for(int c=0; c<3; c++)
  {
     vectorOut[c]=vectorIn1[c]+vectorIn2[c];
  }
}

/********* MATRIX FUNCTIONS *****************************************/
//Multiply two 3x3 matrixs. This function developed by Jordi can be easily adapted to multiple n*n matrix's. (Pero me da flojera!). 
void Matrix_Multiply(float a[3][3], float b[3][3],float mat[3][3])
{
  float op[3]; 
  for(int x=0; x<3; x++)
  {
    for(int y=0; y<3; y++)
    {
      for(int w=0; w<3; w++)
      {
       op[w]=a[x][w]*b[w][y];
      } 
      mat[x][y]=0;
      mat[x][y]=op[0]+op[1]+op[2];
      
      float test=mat[x][y];
    }
  }
}