ZHANG, Ruda September 18, 2021:  Format interpolation notes. [e49bb04]
ZHANG, Ruda December 30, 2018:  Use dollar style math markup. [1b7036c]
Ruda Zhang March 09, 2017:  Add notes on fitting. [647ee47]
Ruda Zhang September 11, 2016:  Completing linear regression model fitting and selection [2f04893]
Ruda Zhang August 03, 2016:  Digitize interpolation methods; organize web map stack. [f3c52c0]