You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: acfModify.m
    path of file: ./repos/toolbox/detector
    
    the code of the file until where you have to start completion: function detector = acfModify( detector, varargin )
% Modify aggregate channel features object detector.
%
% Takes an object detector trained by acfTrain() and modifies it. Only
% certain modifications are allowed to the detector and the detector should
% never be modified directly (this may cause the detector to be invalid and
% cause segmentation faults). Any valid modification to a dete
    
function detector = detectorRescale( detector, rescale )
% Rescale detector by ratio rescale.
opts=detector.opts; shrink=opts.pPyramid.pChns.shrink;
bh=opts.modelDsPad(1)/shrink; bw=opts.modelDsPad(2)/shrink;
opts.stride=max(1,round(opts.stride*rescale/shrink))*shrink;
modelDsPad=round(opts.modelDsPad*rescale/shrink)*shrink;
rescale=modelDsPad./opts.modelDsPad; opts.modelDsPad=modelDsPad;
opts.modelDs=round(opts.modelDs.*rescale); detector.opts=opts;
bh1=opts.modelDsPad(1)/shrink; bw1=opts.modelDsPad(2)/shrink;
% move 0-indexed (x,y) location of each lookup feature
clf=detector.clf; fids=clf.fids; is=find(clf.child>0);
fids=double(fids(is)); n=length(fids); loc=zeros(n,3);
loc(:,3)=floor(fids/bh/bw); fids=fids-loc(:,3)*bh*bw;
loc(:,2)=floor(fids/bh); fids=fids-loc(:,2)*bh; loc(:,1)=fids;
loc(:,1)=min(bh1-1,round(loc(:,1)*rescale(1)));
loc(:,2)=min(bw1-1,round(loc(:,2)*rescale(2)));
fids = loc(:,3)*bh1*bw1 + loc(:,2)*bh1 + loc(:,1);
clf.fids(is)=int32(fids);
% rescale thrs for all features (fpdw trick)
nChns=[detector.info.nChns]; assert(max(loc(:,3))<sum(nChns));
k=[]; for i=1:length(nChns), k=[k ones(1,nChns(i))*i]; end