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From: | Ben Abbott |
Subject: | Re: Polyfit with scaling |
Date: | Thu, 31 Jan 2008 07:47:24 -0500 |
On Jan 31, 2008, at 3:40 AM, Thomas Weber wrote:
The test script uses a set of data for which there is a very small variation in both x and y. As a result, if I make the non-sensical change below; ## scale the x values I still get impressive results warning: dgelsd: rank deficient 13x11 matrix, rank = 3 warning: dgelsd: rank deficient 13x11 matrix, rank = 7 norm difference with normal polyfit: 6.330024 norm difference with wpolyfit: 0.150155 norm difference with new polyfit: 0.082631 It doesn't appear that the example has much comparative value. I suspect that using max(abs(x)) to normalized the x-data will also result in difficulties when that value is substantially large than the other x-data values. I suggest some tests be designed to break both wpolyfit as well as your new version, and see how the three fair comparatively. I'll have some time over the next few days, and will take a shot at writing a few tests myself. Ben |
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