how to test for palindrome of the product of unknown digit numbers

when testing out palindromic numbers for three digit numbers , we could create the products of the three digits this way:

 for i=999:-1:100

    for j=999:-1:100

    answer = i*j;

what if we do not know the number of digit and the number of digit will be the input to the code , how can i adjust the 'for loop' to cater for the unknown number of digits?

say input could be 2 digits or 4 digits or 5 digits and the code will create the products

thanks

Answer 1

[Walter Roberson]

for j = 10^(number_of_digits) - 1 : -1 : 10^(number_of_digits-1)

[OLUBUKOLA ogunsola]

thanks , but is it the same with 'i'?

[Walter Roberson]

Try it.

I have no idea what this has to do with palindromes though. And it probably doesn't matter whether you count forward or count backwards.

[OLUBUKOLA ogunsola]

This returns an empty matrix

[Walter Roberson]

I do not see anywhere in your code where your store anything into a matrix.

I tested my code from number_of_digits = 1 to number_of_digits = 4 and it works fine.

[OLUBUKOLA ogunsola]

@Walter Roberson looking closely at for j = 10^(number_of_digits) - 1 : -1 : 10^(number_of_digits-1) that you earlier suggested actually works, the problem i had earlier with it was placement of the numerous (-1).thanks

Answer 2

[Image Analyst]

Try this:

% Code with a palindrome.
theNumber = 123848321; % A palindrome
str = sprintf('%d', theNumber)
if all(str == fliplr(str))
  message = sprintf('%d is a palindrome', theNumber);
  uiwait(helpdlg(message));
else
  message = sprintf('%d is NOT a palindrome', theNumber);
  uiwait(helpdlg(message));
end

% Code with a non-palindrome.
theNumber = 163848321; % NOT a palindrome
str = sprintf('%d', theNumber)
if all(str == fliplr(str))
  message = sprintf('%d is a palindrome', theNumber);
  uiwait(helpdlg(message));
else
  message = sprintf('%d is NOT a palindrome', theNumber);
  uiwait(helpdlg(message));
end

[OLUBUKOLA ogunsola]

@Image Analyst, what I'm actually trying to do is get all the numbers first before testing for palindrome. I'm trying to get all the possible permutations for n digits number, multiply them then test for palindrome. for example if n is 2( 2 digits number), then ill have numbers like 10,11,12........99. then multiply then against each other. then test the resulting set of numbers for palindrome . the headache here is getting all the permutations .

[Image Analyst]

Then use meshgrid().

[Walter Roberson]

meshgrid() is probably going to use too much memory as the user needs to go to at least 5 digits.

[OLUBUKOLA ogunsola]

well, at this stage of my learning process, memory is not of concern, ill worry about that when i get more comfortable using matlab. ill study meshgrid and give it a try thanks a lot

[OLUBUKOLA ogunsola]

this is what i wrote

function k=multiplication (n)

A= 10^(n-1): (10^n)-1;

B=10^(n-1): (10^n)-1;

for ii= 1: length (A)

      for jj = 1 :length (B)

      k(ii, jj)=ii*jj;

      end 

end 
end

problem now is i get numbers like ’57 ‘ included. what do you think i did wrong here ?

thanks

[Image Analyst]

I don't see any check for whether k(ii,jj) is a palindrome or not. All you're doing is assigning numbers - nothing else.

And what is 57? A, B, ii, jj, or k(ii,jj)?

[Walter Roberson]

k(ii, jj) = A(ii) * B(jj);

[OLUBUKOLA ogunsola]

@Walter , thanks . works now

[OLUBUKOLA ogunsola]

@image Analyst , the goal here is to get the numbers that i will test for palindrome. the testing is up to me now . thanks