ATReturn.taxable: Calculation of after-tax return in a taxable account
In rexmacey/TaxAwareAA: Tax Aware Asset Allocation

The after-tax return calculation in the taxable account is tedious but not complicated. For each year we calculate the income that would be received. The income on an investment (as opposed to what may be received by an investor) grows by a growth rate. The income is taxed based on its character (ordinary, qualified, etc) and the investor's tax rate. Likewise there is capital gains depending on the growth and the turnover. We assume the initial basis equals the initial value (a restriction that could be altered in future version). The basis is updated each period according to sales and purchases. Looping through all the periods of the horizon we arrive at a final income. This income along with the valuation change determines the final value of the asset. This value is adjusted for a final sale assuming any gain (loss) is long-term.

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ATReturn.taxable(yld, growth, valChg, intOrd, intTE, divQual, divOrd,
  turnover, LTCG, STCG, Expense, taxROrdInc, taxRQDiv, taxRLTCG, taxRSTCG,
  taxRState, horizon = 10)

`yld`	Yield on the investment
`growth`	Growth rate of the income paid on the investment
`valChg`	Change in valuation of the investment
`intOrd`	Percent of income taxed at the ordinary rate
`intTE`	Percent of income not taxed
`divQual`	Percent of income taxed at the qualified dividend rate
`divOrd`	Percent of income taxed at the ordinary dividend rate
`turnover`	Percent of asset sold in the current year. Impacts capital gains.
`LTCG`	Percent of capital gains taxed at long-term rate
`STCG`	Percent of capital gains taxed at short-term rate
`Expense`	Annual expense rate
`taxROrdInc`	Tax rate on ordinary income
`taxRQDiv`	Tax rate on qualified dividends
`taxRLTCG`	Tax rate on long-term capital gains
`taxRSTCG`	Tax rate on short-term capital gains
`taxRState`	State income tax rate
`horizon`	Number of year in forecast horizon