TTree::GetMaximum

Hi,

it seems that
Double_t TTree::GetMaximum(const char *columname) is really limited to return maximum of an existing variable in the tree. Is there a function that can return the maximum of an expression from the variables of the tree.
I tried
t->GetMaximum("time*24*3600")
and I got answer 0 without any warnings which is what is should be looking at the code but not what I was expecting.

Thanks

-- 
Nicolas Produit
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