Hi. I'm looking to at how expectation values of periodic functions evolve in time, and i need to prove that <Exp[i[tex]\theta[/tex]]> is continuous in time (this is the expectation of the exponential of the angle). My formula is: <Exp[i[tex]\theta[/tex]]> = Exp[it[tex]/[/tex]2][tex]\sum[/tex]ana*n-1Exp[-int] where an are the fourier coefficients of the initial function, * represents the complex conjugate and the sum is over n from -infinity to infinity. Now how do I go about proving it's continuous? We have basically a complex exponential factor (that's obviously continuous) multiplied by a fourier series, but I just have no idea really where to go from there. Any help would be much appreciated. Thanks!