I am attaching a part of my input script. I get the message that **ERROR: Invalid thermo keyword in variable formula (…/variable.cpp:2008)**

Kindly help me to point out my mistake.

variable N equal atoms

variable ko equal (2.0*v_N)^(1/3)
variable k equal ko*3.1415926535898/lx

variable mx equal -1.0

variable my equal 1.0

variable mz equal 1.0

variable a atom cos(v_k*(v_mx

*x+v_my*y+v_mz*z))

compute b all reduce sum v_a

thermo_style custom step temp press etotal ke c_b pe