`
`Mike Korenberg
`
`From:
`"Mike Korenberg" <korenber@queensu.ca>
`To:
`"Sunny Gupta" <sunny@phasespacesystems.com>
`Sent:
`March 2, 2011 12:01 PM
`Subject: More on noiselessly differentiating the linear combinations of siine & cosines
`Sunny,
`
`
`There's a couple of points about the low-energy component (made from the last, say, 100 terms found by
`FOS) that are interesting. The 1st I already mentioned to you, namely that we can find noiselessly the
`derivative of this component, since it is a linear combination of sine and cosine terms, and this derivative
`can be useful to distinguish the shocked from the non-shocked ICD patients and to view in X, Y, Z space.
`In addition, there are some useful ratios to consider. Thus suppose that u(t), v(t), and w(t) are respectively
`the X, Y, and Z coordinates of the low-energy component and let u'(t), v'(t), w'(t) be their 1st derivatives.
`Then the ratios:
`
`(u'(t)/u(t)), (v'(t)/v(t)), and (w'(t)/w(t))
`
`
`are like Lyapunov exponents and can indicate instability when positive. Consider the regions when the
`ratios are positive, especially when all are. In such regions, the magnitudes of u, v, w will increase. For
`example, if u is then positive, it will grow to a larger positive value because its derivative u' is positive, and
`if instead u is negative it will move downward to a negative value of larger magnitude because u' is
`negative. So these regions will indicate instability, and timing when they occur, and for how long, can be
`good ways of distinguishing shocked from non-shocked ICD patients. Of course, the same discussion
`applies when exponentially-decaying sines and cosines are used, since these can also be noiselessly
`differentiated.
`
`
`Mike
`
`25/03/2011
`
`1
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