On Mar 1, 9:33 pm, "Bart Ogryczak" <[EMAIL PROTECTED]> wrote: > On Feb 28, 10:29 pm, "John Machin" <[EMAIL PROTECTED]> wrote: > > > > > On Mar 1, 4:19 am, "BartOgryczak" <[EMAIL PROTECTED]> wrote: > > > > On Feb 28, 3:53 pm, "John Machin" <[EMAIL PROTECTED]> wrote: > > > > > On Feb 28, 10:38 pm, "BartOgryczak" <[EMAIL PROTECTED]> wrote: > > > > > > [1] eg. consider calculating interests rate, which often is defined as > > > > > math.pow(anualRate,days/365.0). > > > > > More importantly, the formula you give is dead wrong. The correct > > > > formula for converting an annual rate of interest to the rate of > > > > interest to be used for n days (on the basis of 365 days per year) is: > > > > > (1 + annual_rate) ** (n / 365.0) - 1.0 > > > > or > > > > math.pow(1 + annual_rate, n / 365.0) - 1.0 > > > > if you prefer. > > > > YPB? Anyone with half a brain knows, that you can either express rate > > > as 0.07 and do all those ridiculous conversions above, or express it > > > as 1.07 and apply it directly. > > > A conversion involving an exponentiation is necessary. "All those"?? I > > see only two. > > > Please re-read your original post, and note that there are *TWO* plus- > > or-minus 1.0 differences between your formula and mine. For an annual > > rate of 10%, yours would calculate the rate for 6 months (expressed as > > 182.5 days) as: > > math.pow(0.10, 0.5) = 0.316... i.e. 31.6% > > You're assuming that I'd store annual rate as 0.1, while actually it'd > stored as 1.1. > Which is logical and applicable directly.
Storing 1.1 and using it in calculations may save you a few microseconds a day in your real-time apps. However the annual rate of interest is 10% aka 0.1; naming 1.1 as "anualRate" (sic) is utterly ludicrous. -- http://mail.python.org/mailman/listinfo/python-list
