Thread Subject:

Repeating characters

For some work I have to code a function for the Vigenere cipher, I have to make the keyword the same length as my message. so say my message is 'abcdefg' and the keyword is 'at' i need it to repeat the keyword 3 times then have an extra 'a' on the end so it would be 'atatata'. repmat works but only if the message is a multiple of the key, any ideas how i can do this?

"Alice" wrote in message <jkii5v$k7p$1@newscl01ah.mathworks.com>...
> For some work I have to code a function for the Vigenere cipher, I have to make the keyword the same length as my message. so say my message is 'abcdefg' and the keyword is 'at' i need it to repeat the keyword 3 times then have an extra 'a' on the end so it would be 'atatata'. repmat works but only if the message is a multiple of the key, any ideas how i can do this?
- - - - - - - - - - -
 n = length(message);
 m = length(keyword);
 repkeyword = keyword(mod(0:n-1,m)+1);

Roger Stafford

On 3/23/2012 2:16 PM, Alice wrote:
> For some work I have to code a function for the Vigenere cipher, I have
> to make the keyword the same length as my message. so say my message is
> 'abcdefg' and the keyword is 'at' i need it to repeat the keyword 3
> times then have an extra 'a' on the end so it would be 'atatata'. repmat
> works but only if the message is a multiple of the key, any ideas how i
> can do this?

Wrap the logic in a function and use it.

msg='abcdefg';
key='at'

function key=buildkey(msg,base)
   n=fix(length(msg),length(base));
   m=rem(length('abcdefg'),length('at'));
   key=repmat(key,1,n);
   if m>0, key=[key base(1:m)]; end

NB: Air code, untested; salt to suit...

--

Is the keyword always of length 2 or always at least of length 2 but
shorter than 7?

Thanks, Greg G. Kilmer

http://www.panama-foundations.​com/
http://www.panama-inc.com/

http://www.panamataxes.com/
http://www.invest-in-panama.​com/