How does IGOR calculate W_sigma

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Thu, 04/16/2015 - 10:32 pm

I use IGOR to fit functions to data. To gauge what is meant by sigma, i.e. what goes into calculating it, I need to understand how IGOR calculates the W_sigma wave (the sigma for the fitted coefficients). The manual provides a qualitative description but I want to know the math behind it as some programs do things differently (different assumptions etc).