# How can we run many simulations at the same time? (for example for 1000 simulations)

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AT on 31 Dec 2021
Commented: AT on 4 Jan 2022
I wrote this code, but it doesn't work properly for running 10 simulations:
for w=1:10
randn('state',100)
%stoichiometric matrix
V = [-1 1 0; -1 1 1; 1 -1 -1; 0 0 1];
%%%%%%%%%% Parameters andInitial Conditions %%%%%%%%%
nA = 6.023e23; % Avagadro’s number
vol = 1e-15; % volume of system
Y = zeros(4,1);
Y(1) = round(5e-7*nA*vol); % molecules of substrate
Y(2) = round(2e-7*nA*vol); % molecules of enzyme
c(1) = 1e6/(nA*vol); c(2) = 1e-4; c(3) = 0.1;
tfinal = 50;
L = 250;
tau = tfinal/L; % stepsize
counter=0;
T=zeros(L,1);
Exit1=zeros(L,1);
Exit2=zeros(L,1);
Exit3=zeros(L,1);
Exit4=zeros(L,1);
for k = 1:L
a(1) = c(1)*Y(1)*Y(2);
a(2) = c(2)*Y(3);
a(3) = c(3)*Y(3);
d(1) = tau*a(1) + sqrt(abs(tau*a(1)))*randn;
d(2) = tau*a(2) + sqrt(abs(tau*a(2)))*randn;
d(3) = tau*a(3) + sqrt(abs(tau*a(3)))*randn;
Y=Y+d(1)*V(:,1) + d(2)*V(:,2) + d(3)*V(:,3);
counter=counter+1;
T(counter)=counter;
Exit1(counter)=Y(1);
Exit2(counter)=Y(2);
Exit3(counter)=Y(3);
Exit4(counter)=Y(4);
% Recordor plot system state here if required
figure(1)
plot(T,Exit1,'-r')
hold on
plot(T,Exit2,'b-')
hold on
plot(T,Exit3,'-k')
hold on
plot(T,Exit4,'-y')
end
hold on
end
Walter Roberson on 31 Dec 2021
The randn('state') call is forcing the results to be the same for every iteration

Geoff Hayes on 31 Dec 2021
@AT - please clarify what you mean "it doesn't work properly". What are you expecting to happen? Or are you getting the same results on each of the ten iterations because of
randn('state',100)
? I would consider removing this line of code as I think you are resetting the seed to the same value on each iteration of the loop. See Replace Discouraged Syntaxes of rand and randn for details on the behaviour of this function and why you may not want to use it.
AT on 4 Jan 2022
It works. That's exactly what I wanted.
Thanks a million.

Image Analyst on 31 Dec 2021
Your loop is not running your simulations "at the same time". For that you'd need to use "parfor" instead of "for" and have the Parallel Computing Toolbox. Do you have that toolbox? If not, you'll have to run the simulations sequentially (like you're doing now) instead of at the same time.
AT on 4 Jan 2022
@Image Analyst I got it. Thanks a lot.