Using nested for-loop to generate a table of numbers

Question

I try to write a function in which print this output:

1
2 4
3 6 9
4 8 12 16
5 10 15 20 25

I wrote this code, but I'm not getting the desired output:

rows = 5;
% there are 5 rows
for i=1:rows
    for j=1:i
        b=i*j;
    end
    fprintf('%d\n',b)
end

How to I need to correct this algorithm or can you tell me, if there are any other alternate methods to solve this?

Use proper indention and you will notice the obvious error. Your inner loop is not printing anything. — Daniel
– Daniel, Commented Apr 11, 2015 at 11:14

Robert Seifert · Accepted Answer · 2015-04-11 12:14:57Z

2

I don't know what you mean by "print", but this is how you could start:

%// initial vector
a = 1:5;

A = tril( bsxfun(@plus,a(:)*[0:numel(a)-1],a(:)) )
%// or 
A = tril(a.'*a)   %'// thanks to Daniel!
mask = A == 0
out = num2cell( A );
out(mask) = {[]}

A =

     1     0     0     0     0
     2     4     0     0     0
     3     6     9     0     0
     4     8    12    16     0
     5    10    15    20    25

out = 

    [1]      []      []      []      []
    [2]    [ 4]      []      []      []
    [3]    [ 6]    [ 9]      []      []
    [4]    [ 8]    [12]    [16]      []
    [5]    [10]    [15]    [20]    [25]

To print it to a file, you can use.

out = out.'; %'
fid = fopen('output.txt','w')
fprintf(fid,[repmat('%d \t',1,n) '\r\n'],out{:})
fclose(fid)

and you get:

enter image description here

just for the command window:

out = out.'; %'
fprintf([repmat('%d \t',1,n) '\r\n'],out{:})

will be sufficient. Choose your desired delimiter, if you don't like '\t'.

If you insist on a nested for loop, you can do it like this:

rows = 5;
% there are 5 rows
for ii = 1:rows
    for jj = 1:ii
        b = ii*jj;
        if ii <= jj
           fprintf('%d \n',b)
        else
           fprintf('%d ',b)
        end
    end  
end

displays:

1 
2 4 
3 6 9 
4 8 12 16 
5 10 15 20 25

edited Apr 11, 2015 at 12:14

answered Apr 11, 2015 at 11:29

Robert Seifert

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4 Comments

Daniel Over a year ago

No need for bsxfun here, A=tril(a'*a)

Robert Seifert Over a year ago

@Daniel Thanks for the hint, included!

Muhammad Usman Saleem Over a year ago

Thanks thewaywewalk for assistance .. the above mentioned algorithm includes some function with which i am not familiar ... i want to make a script which will create the above mentioned table .... I want to make this script with using nested for loop only... kindly assist me in nested for loop only... thanks

Muhammad Usman Saleem Over a year ago

thank you so much @thewaywewalk for the correct assistance..... :) it absolutely work

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