N = 36;
dx = 1/N
dt = 0.01;
a = 1.4;
initial_eta = 0.;
sum = 0;
u = [1:N+1]*0.;
ux = [1:N+1]*0.;
η = [1:N]*0.;
px = [1:N]*0.;
for i = 1:N;
η[i] = initial_eta;
end;
u[N + 1]= 0;
tau = 1;
T = 86400;
t = 0;
ηbien =  a*sin(2*pi*t)/T;
for tt = 0:30000;
 t = tt/100;
 for i = 2:N;
 px[i]= (η[i]- η[i - 1]) / dx;
 end; px[1] = (η[1]- a*sin(2*pi*t/T)) / dx ;
 for i = 1:N;
 u[i]= u[i]+ dt*(-px[i]- u[i]/tau);
 end;
 for i = 1:N;
  ux[i]= (u[i + 1]- u[i])/dx;
end;
for i = 1:N;
η[i]= η[i] - dt*ux[i];
sum = sum + η[i];
end;