lecture02:
Continuous Fourier Transforms
http://turnbull.dcs.st-and.ac.uk/history/Mathematicians/Fourier.html
http://en.wikipedia.org/wiki/Trigonometric_identity
http://mathworld.wolfram.com/FourierSeries.html
http://www.jhu.edu/~signals/fourier2/index.html
http://cnyack.homestead.com/files/afourtr/ftgauss.htm
http://www.safetyline.wa.gov.au/institute/level2/course18/lecture54/l54_03.asp
http://www.jhu.edu/~signals/convolve/index.html
http://en.wikipedia.org/wiki/Gaussian_integral
http://www.math.sunysb.edu/~tony/tides/analysis.html