我现在在学习用dynare来解DSGE模型，还在初级阶段。按照一些教程写了如下代码可是总是报错"preprocessing failed"，不知道是不是少了什么符号之类的错误。实在是不太熟悉，万望各位大神指点迷津。非常感谢！
var y n i pi a c;
varexo epsilon_a;

parameters sigma phi phi_y phi_pi rho alpha rho_a;

sigma = 5;
phi=2;
rho = 0.9;
alpha = 0.5;
rho_a = 0.7;
phi_pi = 1.5;
phi_y = 1.1;

model;
y = y(+1) - (1/sigma)*(i-pi(+1)-rho);

w - p = sigma*c + phi*c;

w-p = a - alpha*n + log(1-alpha);

sigma*c + phi*c = a - alpha*n + log(1-alpha);

y=c;

y = a + (1-alpha) * n;

a = rho_a * a(-1) + epsilon_a;

i = rho + phi_pi * pi + phi_y * y;
end;

initval;
w=0;
p=0;
y=0;
n=0;
i=0;
pi=0;
a=0;
end;

steady;
check;
shocks;
var epsilon_a = 0.009^2;
end;

stoch_simul(order=1, periods = 500, irf=20, aim_solver);