[milliondreamsblog]

The MIRR Notes formula multiplies by an extra reinvestment factor even though its FV_positive definition already includes reinvestment. Remove that factor, use the magnitude of the negative-flow present value, and define the exponent using the elapsed number of periods, N = len(values) - 1 for one cash-flow series.

Use single backslashes for the LaTeX commands inside the raw docstring so MathJax can render the equation correctly.

For [-120000, 39000, 30000, 21000, 37000, 46000] with finance rate 0.10 and reinvestment rate 0.12, the corrected formula agrees with the function at 12.6094%; the extra factor gives 26.1225%.

This changes only the docstring. Validation: the native package builds on Python 3.13/Linux; all 118 package tests and doctests pass; the Sphinx HTML build passes with -W --keep-going; and the generated MIRR equation and explanation were checked. An AST comparison confirms no executable code changed.