The portfolio object is created with portfolio.spec. The portfolio
object is an S3 object of class 'portfolio' used to hold the initial asset weights,
constraints, objectives, and other information about the portfolio. The only
required argument to portfolio.spec is assets.
number of assets, or optionally a named vector of assets specifying seed weights. If seed weights are not specified, an equal weight portfolio will be assumed.
category_labels
character vector to categorize assets by sector, industry, geography, market-cap, currency, etc. Default NULL