How to display a string in a matrix

so I'm supposed to write a function that takes an input of a string and an integer and then creates a square using the string to make it up and the integer as the dimensions. Here is an example:

square('.',6)
 ......
......
......
......
......
......

this is what I have as code:

   function [ ] = square( s,num )
  square = zeros(num, num);
  for i = 1:num
      for j=1:num

           square(i,j) = s;
        end
     end
     format
     square
    end

my output when I input ('.',6) is

46 46 46 46 46 46
46 46 46 46 46 46
46 46 46 46 46 46
46 46 46 46 46 46 
46 46 46 46 46 46
46 46 46 46 46 46

what am I doing wrong??

Answer 1

[David Goodmanson]

Hi retro, the reason for this is that zeros(n,n), is a matrix of double precision numbers. When you try to insert '.', Matlab converts that string to a number. You can see this with

 >> abs('.')        ans = 46

You have to create a string matrix first. One way to do this is with

m = blanks(9)            % row vector of 9 blanks,  blank = ' '

Then use the "reshape" command to make a 3x3 matrix out of this and proceed as before.

[David Goodmanson]

I also want to mention what 'blanks' is up to. For a row vector of length n:

space = ' ';
vector_of_blanks = space(ones(1,n));

This is known as 'Tony's trick' (Tony Booer, Schlumberger) and it has been around for a long time. It generalizes quite well, so to get an (n x m) matrix of periods:

str = '.';
matrix_of_dots = str(ones(n,m));

Matlab has the 'string' and 'strings' command to deal with this stuff but you tend to end up with double quote marks around every displayed matrix element which is not what you want in this case.