Definition:  for two complexvalued functions, $\underset{\_}{f}$ and $\underset{\_}{g}$, defined on the interval $\left[a,b\right]$ of ℝ, complex number $\langle \underset{\_}{f},\underset{\_}{g}\rangle ={\displaystyle {\int}_{\text{\hspace{0.05em}}a}^{\text{\hspace{0.05em}}b}\underset{\_}{f}(x})\text{\hspace{0.17em}}{\underset{\_}{g}}^{\ast}\text{}(x)\text{\hspace{0.17em}}w(x)\text{d}x$, where w(x) is a real function of x called weight
