Showing that there are particular sequences of functions that converge

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SUMMARY

This discussion focuses on demonstrating the convergence of the sequences \phi_n and \psi_n. The argument establishes that \phi_n converges to a function f by defining \tilde{\phi_n}(x) = \max_{j=1,...,n} \phi_k(x), which remains within 1/n of f and is increasing in n. The properties of \tilde{\phi_n} as a simple function are emphasized, along with the need to prove its increasing nature. The discussion also hints at a similar approach for showing the convergence of \psi_n.

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jdinatale
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That seems like a valid argument for showing that [itex]\phi_n[/itex] converges to f, but I'm not sure how to show it's increasing. And as far [itex]\psi_n[/itex], converges, well I imagine that I'd use a similar argument, but I'm still not sure how to show it's decreasing.
 
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I agree it seems to be missing.

Since [itex]\phi_n[/itex] is smaller than f, you can define
[tex]\tilde{\phi_n}(x) = \max_{j=1,...,n} \phi_k(x)[/tex]
and this will still be within 1/n of f everywhere, and is increasing in n, and each [itex]\tilde{\phi_n}[/itex] is a simple function. Exercise to prove all these properties.
 

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