This function serves as the default example for the buildPortfolios
argument in runMultipleBacktests. It demonstrates how to
construct a list of portfolio specifications using
portfolio.spec,
add.constraint, and
add.objective from the
PortfolioAnalytics package.
Users are encouraged to write their own portfolio list following the same
structure of this function: one input (selected_stocks), one output (a
named list of portfolio.spec objects), and pass it to
runMultipleBacktests() via the buildPortfolios argument.