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Re: NaN error
From: |
Los Griegos Engineering |
Subject: |
Re: NaN error |
Date: |
Wed, 12 Jan 2011 15:01:37 -0600 |
On Tue, 2011-01-11 at 13:52 -0500, John W. Eaton wrote:
> On 11-Jan-2011, Los Griegos Engineering wrote:
>
> | Hello all,
> |
> | I came across the 196 algorithm at:
> | http://mathworld.wolfram.com/196-Algorithm.html
> |
> | I decided to code a version of it, and it works... until I increase the
> | iterations past a limit. I think the error is in the memory, but I'm
> | just not sure where the error is.
> |
> | function [ a ] = rev (a,iter)
> |
> |
> | for k=1:iter
> |
> | a=num2str(a);
> | b=[];
> |
> | for i=length(a):-1:1
> | j=length(a)-i+1;
> | b(j)=a(i);
> | endfor
> |
> | b=str2double(b);
> | a=str2double(a);
> |
> | a=b+a;
> |
> | endfor
> | endfunction
> |
> | The results I get are:
> | octave-3.2.3> rev(123,1)
> | ans = 444
> | octave-3.2.3> rev(123,10)
> | ans = 1354353
> | octave-3.2.3> rev(123,11)
> | ans = NaN
> |
> | octave-3.2.3> rev(12,11)
> | ans = 175857
> | octave-3.2.3> rev(12,14)
> | ans = NaN
> | octave-3.2.3>
> |
> | Is the error due to the memory address of the character array?
> | GNU Octave, version 3.2.3
> | Octave was configured for "i486-pc-linux-gnu".
>
> You can write your function as
>
> function a = rev (a, iter)
> for k = 1:iter
> a = num2str (a);
> b = fliplr (a);
> b = str2double (b);
> a = str2double (a);
> a = b + a;
> endfor
> endfunction
>
> to avoid the inner loop. If I modify it as follows to see what the
> arguments to str2double are, and what the result of the call to
> str2double is
>
> function a = rev (a, iter)
> for k = 1:iter
> a = num2str (a);
> b = fliplr (a);
> bs = char (b)
> b = str2double (b)
> as = char (a)
> a = str2double (a)
> a = b + a;
> endfor
> endfunction
>
> I see
>
> octave> rev (123, 11)
> bs = 627627
> b = 627627
> as = 726726
> a = 726726
> bs = 60+e53453.1
> b = NaN
> as = 1.35435e+06
> a = 1354350
> ans = NaN
>
> so the problem appears to bee that num2str starts returning numbers
> formatted as floating point constants, and when the characters are
> reversed you get something like "60+e53453.1" which is not a number.
>
> Octave doesn't have arbitrary precision integers, so using built-in
> data types here, you will hit a limit at some point no matter what you
> do.
>
> jwe
Thank you for the input. After some more thought, I came up with the
following. It works good as long as I keep the number of digits under
10, i.e. <999999999. I tested the iterations up to 250 with no issues,
other than being very large numbers.
function [ret]=reverseadd(a, iter)
#k controls the number of reveres to add up.
for k=1:iter
n=ceil(log10(a+1));
#Takes each number in "a" and stores it into matrix b size of number of
digits in "a".
for i=1:n
b(i)=(floor(a/10^(n-i)));
a=(a/10^(n-i))-(b(i));
a=a*10^(n-i)#+10^-(1e15);
j=n-i+1;
#Reversing "b"
c(j)=b(i);
endfor
#Takes each element of "b" and "c" and converts it to a number.
d=e=0;
for i=1:length(b)
d=d+b(i)*10^(n-i);
e=e+c(i)*10^(n-i);
endfor
#adds "d" and "e"
a=d+e;
endfor
ret=a;
endfunction
-------------
Blessings,
Roman D. Griego
Los Griegos Engineering
Random Dhammapada Verse: He who has known his former lives and can see
heaven and hell themselves, while he has attained the extinction of
rebirth, a seer, master of transcendent knowledge, and master of all
masteries - that is what I call a brahmin. 423
- NaN error, Los Griegos Engineering, 2011/01/11
- Re: NaN error, Francesco PotortÃ¬, 2011/01/11
- NaN error, John W. Eaton, 2011/01/11
- Re: NaN error, Jordi GutiÃ©rrez Hermoso, 2011/01/11
- Re: NaN error,
Los Griegos Engineering <=