I hate to ask for another function in numpy, but there's an obvious one missing in the financial group: xirr. It could be done as a new function or as an extension to the existing np.irr.
The internal rate of return (np.irr) is defined as the growth rate that would give you a zero balance at the end of a period of investment given a series of cash flows into or out of the investment at regular intervals (the first and last cash flows are usually an initial deposit and a withdrawal of the current balance). This is useful in academics, but if you're tracking a real investment, you don't just withdraw or add money on a perfectly annual basis, nor do you want a calc with thousands of days of zero entries just so you can handle the uneven intervals by evening them out. Both excel and openoffice define a "xirr" function that pairs each cash flow with a date. Would there be an objection to either a xirr or adding an optional second arg (or a keyword arg) to np.irr in numpy? Who writes the code is a different question, but that part isn't hard. --jh-- _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion