This record specifies if the visco-plasticity yielding, for the viscoplastic law with the same index, is used for all values of the yield function (both positive and negative) or only for positive values of the yield function.
If switch is set to -yes then viscoplastic yielding is used for all
values of the yield function 
.
If switch is set to -no then viscoplastic yielding is nonly used for positive
values of the yield function .
If this group_materi_plasti_visco_always record is not specified, the switch is assumed to be -no.
The index specifies the element_group, see element_group.