Indeed, thanks William. I'm not understanding the problem though, as range works with "ordinary" variables:
x=5 [t for t in range(1,x)] Anyway, I changed the units function to not use a list comprehension, and instead use this formula: http://i.investopedia.com/inv/tutorials/site/advancedbond/yield9.GIF The new units function: def units(C, n, F, r): return C * ((1 - (1 / (1 + r) ^ n)) / r) + F * (1 / (1 + r) ^ n) And here we have arrived, successful, with the 3d plot expression: plot3d(price(70,var('n'),1000,var('r')), (n,1,5), (r,0,5)) Hooray sage! Very cool. On Apr 3, 8:53 pm, William Stein <wst...@gmail.com> wrote: > On Fri, Apr 3, 2009 at 7:45 PM, Brian <medo...@gmail.com> wrote: > > > Thank you Timothy. Here is the correct (I believe) code for that > > equation. > > > def units(C, n, F, r): > > return sum([C / (1 + r) ^ t for t in range(1, n+1)]) + F / (1 + r) > > ^ n > > > def price(C, n, F, r): > > return 100 * (units(C, n, F, r) / F) > > > Here, units expresses the equation I linked to, and price gives the > > scaled price, 100 being par. > > > For example, evaluating the expression below demonstrates the example > > calculation from this site: > >http://www.moneychimp.com/articles/finworks/fmbondytm.htm > > > units(70,4,1000,.0853) > > > That evaluates to ~950 as in the example, therefore giving a price of > > ~95: > > > price(70,4,1000,.0853) > > > And sure enough, plotting the price yield curve gives sensible > > results: > > plot(price(70,4,1000,var('y')),0,.2) > > > Now I would like to make a 3d plot where n and r are free. The > > trouble is, when I try it, I get the following error. Would someone > > point out my error? > > > plot(price(70,var('n'),1000,var('y'))) > > > TypeError: range() integer start argument expected, got > > sage.rings.integer.Integer. > > The problem is that you're giving the symbolic variable "n" as input > to the range command (in your units function), but the range command > takes a pair of integers as input. > > William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
