Inverse of a covariance matrix (loop)

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Hi all,
I am stuck to create a loop which yields inverse of covariance matrices.
Data description:
I have the returns of three risky assets: mkt, hml and mom, from nov 3, 1926 up to dec 31, 2012.
For each year (so starting from Nov 3, 1927)I want the inverse covariance matrix for the three risky assets.
The dates are described (thanks Andrei) by the following code:
d = [19261103; 20121231];
ddte = datenum(num2str(d),'yyyymmdd');
ndte = (ddte(1):ddte(2))';
t = weekday(ndte);
ndte = ndte(t ~= 1 & t ~= 7);
yourdata = [date,mkt,hml,mom];
[yy,mm,dd] = datevec(yourdata(:,1));
ymd = [yy,mm,dd];
im = mm == 11 & dd >= 3;
ii = strfind([~im(1),im(:)'],[0 1]);
So I am stuck what do I have to add to retrieve the inverse covariance matrices per year.
Hopefully someone can help me out.
Thanks!
I adjusted the code with cov in it, but it does not yield the desired results:
d = [19261103; 20121231];
ddte = datenum(num2str(d),'yyyymmdd');
ndte = (ddte(1):ddte(2))';
t = weekday(ndte);
ndte = ndte(t ~= 1 & t ~= 7);
yourdata = [date,mkt,hml,mom];
[yy,mm,dd] = datevec(yourdata(:,1));
ymd = [yy,mm,dd];
im = mm == 11 & dd >= 3;
ii = strfind([~im(1),im(:)'],[0 1]);
sb = zeros(numel(ndte),1);
sb(ii) = 1;
sbc = cumsum(sb);
t = sbc > 0 & sbc ~= max(sbc);
sbb = sbc(t);
sb1 = find(sb(t));
wdta = yourdata(t,:);
[r, c] = ndgrid(sbb,1:size(wdta,2)-1);
out1 = accumarray([r(:) c(:)],reshape(wdta(:,2:4),[],1),[],@cov);
out = [ymd(ii(1:end-1),:),out1] ;
What do I do wrong?

Accepted Answer

Andrei Bobrov
Andrei Bobrov on 25 Apr 2013
Try this is code:
d = [19261103; 20121231];
ddte = datenum(num2str(d),'yyyymmdd');
ndte = (ddte(1):ddte(2))';
t = weekday(ndte);
ndte = ndte(t ~= 1 & t ~= 7);
yourdata = [ndte,mkt,hml,mom];
[yy,mm,dd] = datevec(yourdata(:,1));
ymd = [yy,mm,dd];
im = mm == 11 & dd >= 3;
ii = strfind([~im(1),im(:)'],[0 1]);
sb = zeros(size(yourdata,1),1);
sb(ii) = 1;
sbc = cumsum(sb);
t = sbc > 0 & sbc ~= max(sbc);
sb1 = diff(find([sb(t);1]));
wdta = yourdata(t,:);
s = size(wdta,2) - 1;
ydcell = mat2cell(wdta(:,2:end),sb1,s);
out = cellfun(@(x)cov(x)\eye(s),ydcell,'un',0);

More Answers (1)

Kevin van Berkel
Kevin van Berkel on 25 Apr 2013
Andrei you are a legend. Works perfect, thank you very much!

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