Re: Need Help
- To: mathgroup at smc.vnet.net
- Subject: [mg94625] Re: Need Help
- From: dh <dh at metrohm.com>
- Date: Thu, 18 Dec 2008 07:20:12 -0500 (EST)
- References: <gi7lmj$d1m$1@smc.vnet.net> <200812161106.GAA16849@smc.vnet.net> <giao1f$8l6$1@smc.vnet.net>
Hi,
you have a recusrion formula. To get some values for S and R, you do not
need to calculate a close form formula. Simply use the recursion: E.g.
for k=0..11:
B = 8.;
f = 3. 10^-5;
n = 10;
S[0] = 3400;
R[0] = 9;
Do[
S[k + 1] = R[k]*B Random[] - f*S[k]*R[k];
R[k + 1] = f*S[k]*R[k];
, {k, 0, 10}]
hope this helps, Daniel
Oyedeji, Kale wrote:
> Thannks Daniel for your advice. I changed Evaluate to RSolve but still got the same result. What I wanted was a calculation of S[k] and R[k] for every k. I wanted a random number generated for each k. I expect S[1]= some number, R[1]= some number for each k.
>
> Thanks also for calling my attention to CopyAs.Plain Text.
>
> 'Kale
>
> With[{B=8,f=3x10^-5}, sol=RSolve[{S[k+1]==R[k]*B*Table[Random[],{10000}]-f*S[k]*R[k],R[k+1]==f*S[k]*R[k], S[0]==3400, R[0]==9}, {S,R}, {k,0,10000}]]
>
> Sample output:
>
> RSolve[{S[1+k]=={0.561545 R[k]-(3 R[k] S[k])/x10^5,1.80044 R[k]-(3 R[k] S[k])/x10^5,0.901316 R[k]-(3 R[k] S[k])/x10^5,5.51532 R[k]-(3 R[k] S[k])/x10^5,4.2516 R[k]-(3 R[k] S[k])/x10^5,0.949978 R[k]-(3 R[k] S[k])/x10^5,4.13191 R[k]-(3 R[k] S[k])/x10^5,<<9987>>,1.24536 R[k]-(3 R[k] S[k])/x10^5,5.14664 R[k]-(3 R[k] S[k])/x10^5,6.00884 R[k]-(3 R[k] S[k])/x10^5,2.25255 R[k]-(3 R[k] S[k])/x10^5,2.92772 R[k]-(3 R[k] S[k])/x10^5,0.111999 R[k]-(3 R[k] S[k])/x10^5},R[1+k]==(3 R[k] S[k])/x10^5,S[0]==3400,R[0]==9},{S,R},{k,0,10000}]
>
>
> -----Original Message-----
>
> From: dh [mailto:dh at metrohm.com]
> Sent: Tuesday, December 16, 2008 6:06 AM
> Subject: Re: Need Help
>
> Hi,
>
> if you paste output into a mail, you should use CopyAs.Plain Text from
> the Edit menu. I tried to fix your expression:
>
> With[{B=8,f=3
>
> 10-5},sol=Evaluate[{S[k+1]==R[k]*B*Table[Random[],{10000}]-f*S[k]*R[k],R[k+1]=
>
> =f*S[k]*R[k], S[0]==3400, R[0]==9}, {S,R}, {k,0,10000}]]
>
> Please read in the manual about Evaluate, it is not what you want. Look
> at RSolve instead.
>
> Further, you have a recursion formula that contains random numbers????
>
> In addition, instead of a random number you have a vector of random
> numbers??
>
> What are you trying to do???
>
> Daniel
>
- References:
- Re: Need Help
- From: dh <dh@metrohm.com>
- Re: Need Help