Assuming you have that vector already:
M=[ 1 -1 1 -1
1 1 1 -1
-1 1 -1 1 % <----- this row
1 1 -1 1];
a=[-1 1 -1 1];
tmp=abs(M-a);%uses implicit expansion, works in R2016b and newer
tmp=sum(tmp,2) <= eps;
idx=find(tmp);
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