Error messages executing function script

[William Kreamer]

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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