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Re: Amortization Schedule--Global Symbol Value Error

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126591] Re: Amortization Schedule--Global Symbol Value Error
  • From: djorser at comcast.net
  • Date: Mon, 21 May 2012 05:59:40 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

Replace t=j/12; with t[j_]:=j/12; and replace references to t inside of Manipulate to t[j]. 

This will get you numeric values so you can correct your issue concerning incorrect 
values. 

Be sure to do Clear[t] if you have executed t=j/12; 

Don Orser 

----- Original Message -----
From: "waterhand" <sandwaterhand at gmail.com> 
To: mathgroup at smc.vnet.net 
Sent: Sunday, May 20, 2012 2:36:13 AM 
Subject: [mg126591] Amortization Schedule--Global Symbol Value Error 

Let me begin by saying that I am very new to Mathematica, so any help is appreciated. 

I am trying to make an amortization schedule in a table format. The code I have is below: 


*** 

(* psv = Present Value, r = interest rate as a decimal, t = time in years, k = number of payments made *) 
(* mortgage function calculates the monthly mortgage amount *) 
mortgage[psv_, r_, t_] := N[psv*(r/12)/(1 - (1 + r/12)^(-12*t)), 2] 

(* amountLeftOwed function calculates the amount left on the loan including interest *) 
amountLeftOwed[psv_, r_, t_, k_] := N[psv*(1 + r/12)^k - mortgage[psv, r, t]*((1 + r/12)^k - 1)/(r/12), 2] 

(* paidInInterest function calculates the amount of the mortgage payment that goes towards the interest *) 
paidInInterest[psv_, r_, t_, k_] := N[amountLeftOwed[psv, r, t, k]*r/12, 2] 

(* paidInPrincipal function calculates the amount of the mortgage payment that goes towards the principal *) 
paidInPrincipal[psv_, r_, t_, k_] := N[mortgage[psv, r, t] - paidInInterest[psv, r, t, k], 2] 

(* remainingBalance function gives the remaining balance after payment has been made *) 
remainingBalance[psv_, r_, t_, k_] := N[amountLeftOwed[psv, r, t, k] - mortgage[psv, r, t], 2] 

(* j is the number of months. this converts months to years *) 
t = j/12; 

Manipulate[ 
TableForm[ 
Prepend[ 
Table[{i, paidInInterest[psv, r, t, i], paidInPrincipal[psv, r, t, i], remainingBalance[psv, r, t, i]}, {i, 1, j}], 
{"Month", "Interest", "Principal", "Balance"}]], 
{{psv, 100000, "Loan Amount"}, 100, 200000, 100}, {{r, 0.05, "Interest Rate"}, 0.01, .1, 0.0005}, 
{{j, 120, "Number of Months"}, {120, 240, 360}} 
] 

*** 

Here's the issues I am having: 

1) The variable j is coming up with the "Global symbols that have no assigned value" error despite it being assigned 120, 240, and 360 in the Manipulate[] function. When I add a line like "j = 120", the code "works". The reason for the quotations is explained in number 3 below. 
2) Despite the N[*, 2] function, the numbers are coming out as scientific notation. Even with the line j = 120, the rounding is not to two places. 
3) The table should end with the ending balance being zero. When I force the value of j (again, j = 120, 240, or 360), I am getting a negative value for the last two months. Is there a rounding issue related to #2? 

Again, very new to Mathematica. I appreciate any help. 

Thanks for reading, 

Mike 



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