Sorry I didn't clarify that: I define the initial random positions, I
store them in a variable, say pos_in, and then I call the functions (the
different versions) with pos_in as input, so the initial positions are
the same in every case.
On 28/01/13 14:07, Serge Steer wrote:
If the initial position of your sphere are randomly set, it can be
normal than you do not have the same number of iteration from one
simulation to an other one.
can you check using
rand("seed",0)
to force identical initial points for your various tests.
Serge Steer
Le 28/01/2013 16:18, Ezequiel Soulé a écrit :
The algorithm essentially starts with a set of spheres in random
positions and in a relatively dense state, and runs an iterative
process where the spheres are moved in each iteration in order to
reduce the overlaps.
The core of the script is more or less like this
superp=calc_D_superp_dobcel(pos); //this line uses an external function
to calculate a matrix with the overlap between paritcles, defined as
superp(i,j)=max(R(i)+R(j)-D(i,j),0) . D(i,j) is the distance between the
spheres and R is the radius. pos is a 3-colum matrix containging the
coordinates of the position of each sphere
control=0; //number of iterations
sup_2(int(control/max_mov*20)+1)=sumsupant/max_mov*20; // this defines a
third control system as will be described bellow. **
while max(superp)>tol // the maximum value of superp controls when the
system is considered overlap-free and the algorithm is finished
...
// Several lines where the positions of each sphere are modified, acording to
the values of the matrix superp
...
superp=calc_D_superp_dobcel(pos); //matrix superp is re-calculated with the new positions
control=control+1;
if control>max_mov then break; end // control by maximum number of
iterations
//the following belongs to the third control system:
if length(sup_2)==int(control/max_mov*20) then sup_2(int(control/max_mov*20)+1)=sum(superp)/max_mov*20; //**
else//**
sup_2(int(control/max_mov*20)+1)=sup_2(int(control/max_mov*20)+1) +
sum(superp)/max_mov*20; //**
end //**
if length(sup_2)>4.5 then //**
if sup_2($-1)>0.85*sup_2($-2) & sup_2($-2)>0.85*sup_2($-3) then
break; end //**
if sup_2($-1)>0.7*sup_2($-2) & sup_2($-2)>0.7<
span styl
e="color:rgb(92,92,92)">*sup_2($-3) & sup_2($-3)>0.6*sup_2($-4) then break;
end //**
end //**
end//ends while loop
The third control system essentially controls if the overlap is
decreasing as the iterations proceed. It defines a new variable,
sup_2, that stores the average value of sum(superp) in max_mov/20
iterations. If this average does not decrease fast enough (>15%
decrease in two or >30%decrease in three consecutive groups of
max_mov/20 iterations), it considers that it will not converge and
breaks.
Now, this third control system seems to be problem. As you can see,
non of its lines (marked with ** for more clarity), affects the
values of superp (at least, it shouldn´t). But still, the value of
superp is modified when I include this control system.
The other problem I had was with a similar algorithm, without the
third control system, but just adding a "pause" rigth after the last
end. This will also modify the values of superp and the number of
iterations.
As I said, the error in superp is not important (it is in the order
of 1.d-15), but this difference propagates exponentially through the
iterations and can significantly modify (like a 30%) the total number
of iterations (I was trying to evaluate if the third control really
worked, but I couldn´t do it because the algortihm CONVERGES with a
different number of iterations...)
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