Is rate method similar to MS-Excel RATE() function?

[c-castillo]

I need to implement the excel RATE() function to do some financial calculus. I didn't understand both MS documentation and this gem documentation, so... is rate method the ruby implementation of that Excel function?

[wkranec]

Finance::Rate is an object representing an interest rate.

Based on my understanding, Excel's RATE() function returns an interest rate, based on some number of constant payments and a present value. I think of it as a higher-level IRR() function (which can be accessed in Finance via Array#irr).

Excel: RATE(10,500,-200000) #=> -0.398102343635752

Now set C4 = 200000, and C5:C14 = -500: IRR(C4:C14) #=> -0.398102343635752

Finance: [200000,-500,-500,-500,-500,-500,-500,-500,-500,-500,-500].irr #=> -0.398102343635752

That last line should work, but doesn't ... I'll have to do some digging as to why. Otherwise, we could implement excel's functionality quite easily:

def excelRATE(num, payment, present_value)
  cashflow = [] << present_value
  num.times do
    cashflow << payment
  end
  cashflow.irr
end

I'll post again when I can get this example working properly.

Thanks, Bill

[c-castillo]

Bill, thanks a lot! Your examples helped me to understand the Rate function. I run a couple of tests in both Excel and irb console, and in some cases the values match, but in some cases it doesn't. I'm trying to figure out why.

Thanks again!

[marksweston]

Closing due to age.