Hi everyone,

I want to calculate the maximum shear stress and find that there is some wrong with the angle θ in the formula as it need to calculate the acos(x),like this command,

variable O atom “acos(v_R/sqrt(-1*v_Q)^3)”

the result said that

ERROR: Invalid syntax in variable formula (…/variable.cpp:3139)

I tried to change the denominator to forbid the v_O overflows from -1 to 1, but it still doesn’t matter. How do you resolve this problem or is there any other solution to calculate the maximum shear stress.

Best wishes!

Hi everyone,

I want to calculate the maximum shear stress and find that there is some

wrong with the angle θ in the formula as it need to calculate the

acos(x),like this command,

variable O atom "acos(v_R/sqrt(-1*v_Q)^3)"

the result said that

ERROR: Invalid syntax in variable formula (../variable.cpp:3139)

i cannot reproduce this error from the formula above. the error message

indicates that you may have mismatched parenthesis. please carefully

check, that your input is using the exact same formula and that all symbols

and characters are ASCII.

axel.

Hi Axel,

Thank you for your suggestion and I have solved this problem successfully, but I met another problem, I need to choose the maximum principle stress and the minimum principle stress use the command

variable st1 atom max(v_R1,v_R2,v_R3)

variable st2 atom min(v_R1,v_R2,v_R3)

while the output error detail is

ERROR: Invalid special function in variable formula (…/variable.cpp:3903)

I think that maybe the reason the max() function output the scalar not the vector leading to which cant dump it, so what can I do to make it

Best wishes!

Hi Axel,

Thank you for your suggestion and I have solved this problem successfully,

but I met another problem, I need to choose the maximum principle stress

and the minimum principle stress use the command

variable st1 atom max(v_R1,v_R2,v_R3)

variable st2 atom min(v_R1,v_R2,v_R3)

while the output error detail is

ERROR: Invalid special function in variable formula (../variable.cpp:3903)

http://lammps.sandia.gov/doc/variable.html