Hi,

I'm trying to calculate a tetrahedral volume using a Topas macro. Of course this can be done with Vesta but it won't give an error.

I've written this macro (using the Cayley-Menger determinant):

macro calc_tetrahedral_volume(dist1,dist2,dist3,dist4,dist5,dist6, c, vol_calc)
{
   #m_ifarg c ""
      #m_unique_not_refine c
   #m_endif
	prm = Sqrt((1/144)*(4*(dist1^2)*(dist2^2)*(dist3^2) - (dist1^2)*((dist5^2) + (dist6^2) - (dist4^2))^2 - (dist2^2)*((dist4^2) + (dist6^2) - (dist5^2))^2 - (dist3^2)*((dist4^2) + (dist5^2) - (dist6^2))^2 + ((dist1^2) + (dist2^2) - (dist4^2))*((dist1^2) + (dist3^2) - (dist5^2))*((dist2^2) + (dist3^2) - (dist6^2)))); : vol_calc
}

where dist1 through dist6 are edge distances of the tetrahedron. I get them like this:

Get_Distance(Mn1 0 0 0 0 O1 17      1   0   0, Mn1_O_1,  1.88002555`_0.00475797999)
Get_Distance(Mn1 0 0 0 0 O1 12      0  -1   0, Mn1_O_2,  1.88002555`_0.00475797999)
Get_Distance(Mn1 0 0 0 0 O1 30     -1   0   1, Mn1_O_3,  1.88002555`_0.00475797999)
Get_Distance(Mn1 0 0 0 0 O1 25      0   1   1, Mn1_O_4,  1.88002555`_0.00475797999)
Get_Distance(Mn1 0 0 0 0 O1 32      0   1   1, Mn1_O_5,  1.88002555`_0.00475797999)
Get_Distance(Mn1 0 0 0 0 O1 14      0   0   0, Mn1_O_6,  1.88002555`_0.00475797999)

Get_Distance(O1 17 1  0  0 O1 12  0 -1  0, Mn1_O1_O2, 2.53267539`_0.00831199349)
Get_Distance(O1 17 1  0  0 O1 30 -1  0  1, Mn1_O1_O3, 3.7600511`_0.00951595999)
Get_Distance(O1 17 1  0  0 O1 25  0  1  1, Mn1_O1_O4, 2.77912569`_0.00827719217)
Get_Distance(O1 17 1  0  0 O1 32  0  1  1, Mn1_O1_O5, 2.77912569`_0.00827719217)
Get_Distance(O1 17 1  0  0 O1 14  0  0  0, Mn1_O1_O6, 2.53267539`_0.00831199349)

Get_Distance(O1 12 0 -1  0 O1 30 -1  0  1, Mn1_O2_O3, 2.77912569`_0.00827719217)
Get_Distance(O1 12 0 -1  0 O1 25  0  1  1, Mn1_O2_O4, 3.7600511`_0.00951595999)
Get_Distance(O1 12 0 -1  0 O1 32  0  1  1, Mn1_O2_O5, 2.77912569`_0.00827719217)
Get_Distance(O1 12 0 -1  0 O1 14  0  0  0, Mn1_O2_O6, 2.53267539`_0.00831199349)
Get_Distance(O1 30 -1 0 1 O1 25  0  1  1, Mn1_O3_O4, 2.53267539`_0.00831199349)
Get_Distance(O1 30 -1 0 1 O1 32  0  1  1, Mn1_O3_O5, 2.53267539`_0.00831199349)
Get_Distance(O1 30 -1 0 1 O1 14  0  0  0, Mn1_O3_O6, 2.77912569`_0.00827719217)
Get_Distance(O1 25 0 1 1 O1 32  0  1  1, Mn1_O4_O5, 2.53267539`_0.00831199349)
Get_Distance(O1 25 0 1 1 O1 14  0  0  0, Mn1_O4_O6, 2.77912569`_0.00827719217)
Get_Distance(O1 32 0 1 1 O1 14  0  0  0, Mn1_O5_O6, 3.7600511`_0.00951595999)

I then call the calculation like this:

calc_tetrahedral_volume(Mn1_O_1, Mn1_O_2, Mn1_O_3, Mn1_O1_O2, Mn1_O2_O3, Mn1_O1_O3, vol1,0)

However, this always gives me Exception Caught. I would assume this is because the Sqrt() is getting a negative number, and I've tested by removing the Sqrt and it then works. I've also tested setting the 6 distance params as an arbitrary number (i.e. 1) and it then works and gives the correct volume for such a tetrahedron. So the code does work.

However, the thing is, it should work with the distances I set. You can tell from the Get_distance calls that the distances are that of a real tetrahedron. I've written the same algorithm in Python ( https://github.com/lnaglecocco/VanVleckCalculator ) and it works there.

Has anyone attempted anything like this before and has a suggestion?