= Window function
{title2=$w_T(t)=\mathbf1_{[0,T]}(t)$}
{wiki}
A window function is a <function> that vanishes outside a chosen finite <interval>; multiplying an input by it selects and weights that part of the history before a <Fourier transform>. The rectangular window $w_T$ is the <indicator function> of $[0,T]$. Applied to the weighted <causal extension by zero> of an input, it produces the finite-history <integral> $\int_0^T e^{-st}f(t)\,dt$ used to approximate a <Laplace transform>.
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