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

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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

##### 1 Comment

Walter Roberson
on 31 Dec 2021

The randn('state') call is forcing the results to be the same for every iteration

### Accepted Answer

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.

### More Answers (1)

Image Analyst
on 31 Dec 2021

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