Hi all. I am learning a numerical method that involves Fourier transform. As far as I know, I think Fourier transform is tool to find the frequency spectrum of a signal. And the usual form shall be "Integrate from negtive infinity to positive infinity, f(x)*exp(i*w*x)dx" However, when i search this in wikipedia, it is defined with (w-wo), where wo is the central frequency. http://en.wikipedia.org/wiki/Split-step_method I don't really know what this definition is doing and what changes it would bring. Why is it necessary to do so? Please help.