Just a small problem

Hi! Can you help me please with this problem: How can I Write a function that produces random integers From 1000 to 9999, and including the numbers of different 4-digit (with no repetition)? In MatLab...

[Andrew Newell]

For a start, see randint: http://www.mathworks.com/help/toolbox/comm/ref/randint.html.

[Izmir]

I need the program as soon as possible.... Please help me????? :(

Answer 1

[Fangjun Jiang]

function y=MyRandInt
while true
    y=floor(8999*rand+1000);
    if length(unique(num2str(y)))==4
        return;
    end
end

[Izmir]

Thanks very Much!!!!!

[Izmir]

How to save the .m file to bring it back by a command?

[Fangjun Jiang]

Save the above code into MyRandInt.m and put it in your current folder or any where in the MATLAB path, then run MyRandInt at the Command Window.

[Izmir]

Ok. Thanks!!! :)

[Izmir]

Is it possible to write the different program with the same function?

[Izmir]

Can you also comment the lines of the program?

function y=MyRandInt

while true

y=floor(8999*rand+1000);

if length(unique(num2str(y)))==4

return;

end

end

[Walter Roberson]

Do you need the functionality "as soon as possible", or do you need someone to complete an assignment for you "as soon as possible"?

If you need the functionality, you have it. If this is an assignment, then you should write your own code -- or at the very least do your own analysis of how the code works.

[Fangjun Jiang]

If you don't understand any function or keywords, such as while, true, floor, rand, length, unique, num2str, return, etc. type the following to get the help document

help while

doc while

help floor

doc floor

...

[Izmir]

I made it. Now no problem... I'm beginner in MatLab, that's why...

[Jan]

Even, or especially, a beginner has to read the Getting Started chapters of the documentation. You cannot use such a powerful language like Matlab without spending the time to learn the basics.

[Fangjun Jiang]

It took me more than 30 minutes to come up with the answer. 20 minutes for thinking about whether it is a homework assignment. At the end, I think it is not. 10 minutes for thinking about which approach is better, the permutation method or the try-and-error method.

I would not think this is a homework assignment for an entry level MATLAB class. Think about it, what aspect of the language (programming flow, for-loops, or if-else statment) would be a good fit to solve this problem?

Jan has been an A+ student here. But I would grade all three of his homework a B+. Which entry level class or beginner student would use randperm() or perms()? I would expect brutal force if b(4)~=b(3) && b(4)~=b(2) && b(4)~=b(1) ... etc.

Answer 2

[Jan]

Finite and no large table:

a      = 0:9;
i1     = ceil(rand * 9);
a(i1 + 1) = [];
p      = randperm(9);
result = i1 * 1000 + a(p(1:3)) * [100; 10; 1]

[Fangjun Jiang]

B+

[Daniel Shub]

This is how I would have done it.

Answer 3

[Jan]

It really looks like a homework and your teacher/professor will not recommend this forum to other students any longer after your homework has been solved here. Be sure to mention the assistence you got, otherwise it would be cheating.

I'd prefer a solution, which is guaranteed to stop in finite time. But I have only this idea:

a = 0:9;
while true
  b = a(randperm(10, 4));   % Matlab 2011b required
  if b(1) ~= 0
    break;
  end
end
result = b * [1000; 100; 10; 1]

For earlier Matlab versions:

b = a(randperm(10));
...
result = b(1:4) * [1000; 100; 10; 1]

[Fangjun Jiang]

B+

Answer 4

[Jan]

An algorithm in finite time, but not really efficient:

K = perms(0:9);
K(K(:,1) == 0, :) = [];
index  = ceil(rand * size(K, 1));
result = K(index, 1:4) * [1000; 100; 10; 1]

It is more efficient to create a [Nx4] table only instead of the [Nx10] table of perms:

K = VChooseKO(0:9, 4);

See: FEX: VChooseKO. But even then the large table is brute.

[Fangjun Jiang]

B+