diff --git a/SRI_matlab/main.m b/SRI_matlab/main.m
index ac9f50d13a54bb2a9cb13d19d9acc2511e61dcdb..9064c7e25260df116b4dc204f9e49ee860ddc27e 100644
--- a/SRI_matlab/main.m
+++ b/SRI_matlab/main.m
@@ -1,22 +1,22 @@
 clear figure
 
 S = 990;
-I = 10;
+I = 50;
 R = 0;
 n_pop = S + I + R;
 
 input = [S, I, R];
 
 coeffs = options;
-coeffs.InfectionRate = 0.06;
-coeffs.ImmunisationRate = 0.01;
+coeffs.InfectionRate = 0.09;
+coeffs.ImmunisationRate = 0.005;
 coeffs.ImmunisationLossRate = 0.001;
 coeffs.VaccinationRate = 0.02;
 coeffs.DeathRate = 0.04;
 coeffs.NaturalDeathRate = 0.002;
 coeffs.NatalityRate = 0.003;
 
-N = 30;
+N = 1000;
 
 Slist = zeros(1, N);
 Ilist = zeros(1, N);
@@ -28,7 +28,7 @@ for i=t
     Slist(i) = input(1);
     Ilist(i) = input(2);
     Rlist(i) = input(3);
-    input = step(input, coeffs)
+    input = step(input, coeffs);
 end
 
 % figure
diff --git a/SRI_matlab/step.m b/SRI_matlab/step.m
index 8cb17c9884d2df624f5e0d61f2fa5a865765ca3d..8e1f987ace602053be54af608cdcf175bf681a0d 100644
--- a/SRI_matlab/step.m
+++ b/SRI_matlab/step.m
@@ -5,7 +5,7 @@ R = X(3);
 
 N = S + I + R;
 
-dS = -options.InfectionRate * S * I/N - options.VaccinationRate * S + options.ImmunisationLossRate * R + options.NatalityRate - options.NaturalDeathRate * S;
+dS = -options.InfectionRate * S * I/N - options.VaccinationRate * S + options.ImmunisationLossRate * R + options.NatalityRate * N - options.NaturalDeathRate * S;
 dI = options.InfectionRate * S * I/N - options.ImmunisationRate * I - options.DeathRate * I;
 dR = options.ImmunisationRate * I + options.VaccinationRate * S - options.ImmunisationLossRate * R - options.NaturalDeathRate * R;