From help-octave-request at bevo dot che dot wisc dot edu Tue Jan 22 09:23:20 2002
Subject: Re: Error messages executing function script
From: Benjamin Bunck <bbunck at riemann dot math dot twsu dot edu>
To: William Kreamer <kreamer at 954access dot net>
cc: help-octave at bevo dot che dot wisc dot edu
Date: Tue, 22 Jan 2002 09:31:07 -0600 (CST)


FWIW, I tried this on 2.0.16 (I know, old!) and it worked, once 

Divisor += 2;

was changed to:

Divisor = Divisor + 2;

That is to say, is_prime(29) returned 1 on the first try.  What verion of 
Octave under what OS are you using?


Ben


On Tue, 22 Jan 2002, William Kreamer wrote:

> The script included in this email is a working function to determine whether
> a given number is prime. However, when I first run it, inputting a number
> such as 29.0, I get the error messages:
>   can't perform indexing operation for <unknown type> type
>   evaluating assignment expression near line 3, column 3
> 
> When I run the script again, it works perfectly. Please help.
> 
> #This Octave function script will take a number passed to it
> #determine whether it is prime.
> 
> function y = is_prime (x)
> y = 0;
> x = abs(x);
> if (x < 1)
>     Quot = 0;
>     Leftover = 0;
>     y = 0;
>     return;            #exits the function
> endif
> x = floor(x);
> Dividend = x;
> Divisor = 2;
> while(Dividend >= Divisor)
>     Quot = floor(Dividend / Divisor);
>     Leftover = rem(Dividend, Divisor);
>     if (Leftover != 0)
>          break;
>     endif
>     Dividend = Quot;
> endwhile
> Divisor = 3;
> while(Quot >= Divisor)
>     Quot = floor(Dividend / Divisor);
>     Leftover = rem(Dividend, Divisor);
>     if (Leftover == 0)
>         Dividend = Quot;
>         continue;
>     endif
>     Divisor += 2;
> endwhile
> if (Dividend == x)
>     y = 1;
> elseif (x == 2)
>     y = 1;
> endif
> endfunction
> 
> 
> 
> 
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Octave is freely available under the terms of the GNU GPL.

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