Question about the NK model using Dynare

Hello everyone.

I’m writing NK model in Dynare and always encounter the problem like:
ERROR: in the ‘steady_state_model’ block, variable ‘a’ is undefined in the declaration of variable ‘y_n’
Preprocessing time: 0h00m00s.

I have no idea about the error for I have already defined the a variable above. Please help me.
Best
NK_stickyprice.mod (8.1 KB)

No, you set a=0 in initval, but that is meaningless for steady_state_model.