Moreover, if I understand correctly, the OP is asking for a definition of a financial term. I'd expect instead that for a financial question to be suitable, it had to be rephrased in terms understandable to mathematicians. I'm not competent to judge whether the jargon used by the OP is standard or not in financial mathematics (I guess "portfolio" is, but I'd be surprised if there existed a single notion of "portfolio distance" without further qualifications).
]]>There is a comment in the question saying «I doubt many hear will even understand the subject concerned». I hope this is not taken as grounds for closing: that criterion would leave us with very few questions!
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