I want to use the random walk simulation A + A=0 of the chemical reaction, here is my code I use 0 Spaces, 1 represents the particle grid; 1 + 1=0
clear; CLC

IterMax=20.

Nx=10;

Ny=10;

M_0=10; % the number of particles initial

A=zeros (Nx, Ny);

N=Nx * Ny;

% linear index S

Ind=sub2ind (size (A), 1: Nx, 1: Ny);

The index=randperm (N, M_0); % choose 10 element in A randomly

A (index)=1

S=find (A==1);
% of each particle seat
M=zeros (1, iterMax);

M (1)=M_0;

R=zeros (1, iterMax);

R (1)=0.25;

I=fix (r. * M) + 1;

For n=1: iterMax

For j=2: iterMax

R (j)=rand (1);

End

If (0 & lt; R (n)) & amp; & (r (n) & lt;=0.25)

DS=- Ny;

If (S (I) + dS) & lt;=N & amp; & (S (I) + dS) & gt; 0

If A ((S (I) + dS)==0)

A (S) (I)=0;

A (S (I) + dS)=1;

S (I)=S (I) + dS;

M=M (n) (n + 1);

The else

A (S) (I)=0;

A (S (I) + dS)=0;

K=find (S==S (I) + dS);

S (k)=[];

S (I)=[];

M=M (n) (n + 1) - 2;

If M (n + 1) & lt; 0

Break

End

End

The else

S (I)=S (I);

M (n + 1)=M (n)

End

Elseif (0.25 & lt; R (n)) & amp; & (r (n) & lt;=0.5)

DS=Ny;
,,,
Error:

Why in addition to the M (1)=10, other M 0 loop is what went wrong?