with it being empty, end as an index would be 0. mTtot(end) would be mTtot(0) which is not permitted.
mTtot= [mTtot ,t.'+mTtot(end)+resol];
Perhaps you are wanting mTtot(end) to be empty instead of an error when mTtot is empty. But if that were the case, then you would have the situation
mTtot = [, t.'++resol]
and anything +  is , so you would be dealing with
which would leave mTtot empy, but I suspect you are trying to append to it in that statement,.