Combining absolute values of response is done by operator type VAR_OPER
= SUB_ABS. To get the absolute value of the difference of two
terms (DRESP_1 and DRESP_2) the design
response definition is as follows:
DRESP
ID_NAME = .....
DEF_TYPE = OPER
VAR_OPER = SUB_ABS
VAR_A = DRESP_1
VAR_B = DRESP_2
END_