Error using - Matrix dimensions must agree. Error in WDO_SG_Code_PL_test1m (line 322) a2=aa-a1;?

i have an index file having stereo=[1 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1]; and aa=find(stereo); now index is refered in my main code file as

u(hour)=hour; Clothesdrye(hour)=power_pattern(hour,1); a1=find(Clothesdrye); Index a2=aa-a1; %a3=sum((a2)/9); b2=bb-b1;

Error using - Matrix dimensions must agree.

Error in WDO_SG_Code_PL_test1m (line 322) a2=aa-a1;