How do I generate a given Matrix in one command?

I have to generate a matrix A = [1 1 0 0 0; 1 1 1 0 0; 0 1 1 1 0; 0 0 1 1 1; 0 0 0 1 1]

writing a single command.

Teacher told as some helpful commands would be

 EYE(m,n)     
 ONES(m,n)
 ZEROS(m,n)
 RAND(m,n)

I give you a beer

[Jan]

As you can see in the web interface at several positions: The name of Matlab is "Matlab".

Do you think, that the answer help you? Or will they just amuse your teacher?

[Jan]

For clarification: Does "I give you a beer" belong to the list of helpful commands or is this a different topic?

[Paulo Silva]

+1 vote to marciuc just because of the beer :)

[Jan]

+1: If you can explain how all solutions given here work, you will pass the complete Matlab course based on just one question. Every single answer is funny, but all answers together are serious.

Answer 1

[Jan]

Refering to your former post, which has been deleted now: I know also, who you are: you are marciuc.

At first I suggest this:

A = [1 1 0 0 0;1 1 1 0 0;0 1 1 1 0;0 0 1 1 1;0 0 0 1 1]

This is a single command and it is the most efficient solution: No temporary memory, no overhead for calling commnad, and easy to debug. There is no better solution.

[Jos (10584)]

vote +1

Answer 2

[Sean de Wolski]

Probably the most compact:

 A = toeplitz([1 1 0 0 0])

[Jan]

This is the most compact command, except for the ambitious RAND apporach. I vote it.

Answer 3

[Jan]

Give the beer to your teacher. He is obviously funny if he suggests RAND - but it really works:

A = round(rand(5))

There is at least a certain chance to get the correct answer.

[Matt Fig]

Always a sense of humor.

[Andrew Newell]

A = randint(5) would be a shorter way of maybe getting the right answer!

[Jan]

You need the Communications Toolbox for RANDINT.

[Andrew Newell]

A small price to pay for elegance!

[Jiro Doke]

Or if you have MATLAB R2008b or newer,

A = randi([0 1], 5)

Answer 4

[Jan]

A = dec2bin([24 28 14 7 3]) - '0'

[Jiro Doke]

+1 vote!

[Matt Tearle]

That is sick, wrong, disturbing, and I love it

[David Young]

dec2bin('vzlea'-'^')-'0'

[Jan]

There is the vuvuzela again. The question is obviously more diabolic than I've expected. Again you see: Subtracting zero can reveal the clandestine information.

Answer 5

[Matt Tearle]

A = full(gallery('tridiag',ones(1,4),ones(1,5),ones(1,4)))

But my current favorite:

A = 1-reshape(mod(floor((1:25)/3),2),5,5)

[Sean de Wolski]

Nice job with your current favorite!

Answer 6

[Kenneth Eaton]

I can't believe no one suggested dilation:

A = imdilate(eye(5),ones(2));

Or convolution:

A = sign(conv2(eye(5),ones(2),'same'));
A = sign(filter2(ones(2),eye(5)));

[Jan]

*You* have suggested it now. So I can't believe it now, too. +1

Answer 7

[Jan]

A general method to create a diagonal matrix is using DIAG (as the example in "help diag" explains):

A = diag(ones(1, 5)) + diag(ones(1,4), 1) + diag(ones(1,4), -1);

You can discuss, if this is still "a single command".

I do not drink beer. But you can ask your teacher to send me the points gained by solving this homework.

[Sean de Wolski]

Can I have your beer ?!

[Matt Tearle]

You can have all the beer that marciuc's teacher sends me. How's that for a deal?

Answer 8

[Paulo Silva]

Here's probably the most awesome way to generate the matrix :D

disp('I dare you to try the Infinite monkey matrix')
answer=input('Press y and Enter if your dare to try','s')
if (strcmp(answer,'y'))
disp('Congratulations your are not a coward')
disp('Good luck')
pause(1)
disp('Please wait or press CTRL+C to cancel')
disp('but canceling the operation makes you a coward!!')
a=[1 1 0 0 0; 1 1 1 0 0; 0 1 1 1 0; 0 0 1 1 1; 0 0 0 1 1];
w=0;b=zeros(5,5);
while ~isequal(a,b)
b=randi([0 1],5,5);
w=w+1;
end
disp('Congratulations we found the Infinite monkey matrix for you')
b
disp('after')
w
disp('attempts')
else
disp('You are a coward!!!!')    
end

[Sean de Wolski]

Yay! The infinite monkey makes its second appearance in a week.

Answer 9

[Walter Roberson]

EDIT: line-broken per request.

eval(char(mod(1.0599.^ ...
'i<o<ZC<C<d<d<d_C<C<C<d<d_d<C<C<C<d_d<d<C<C<C_d<d<d<C<Cv', ...
96)))

[Jan]

Thanks for line breaking. This solution will drive marciuc's teacher crazy. Such ugly! +1

Answer 10

[Jan]

A = abs(bsxfun(@minus, 1:5, transpose(1:5))) < 2

Answer 11

[Jan]

A = 1 - (tril(ones(5), -2) + triu(ones(5), 2))

Answer 12

[Jan]

I cannot resist to post some variation of the DEC2BIN theme:

A = dec2bin('8<.''#' - 32) - '0'

A = dec2bin('FJ<51' - 46) - '0'

But finally you can even omit the first subtraction, because DEC2BIN operates on CHAR vectors also, but you cannot type the non-printables directly:

q = [100 101 99 50 98 105 110 40 39 24 28 14 7 3 39 41 45 39 48 39];
clipboard('copy', char(q))
==> Ctrl-v in the command window
>> dec2bin('#####')-'0'

Here the '#' are the non-printables with the ASCII codes [24,28,14,7,3]. You can write them even in a M-file.

Answer 13

[Paulo Silva]

b=[0     0     1     1     1
   0     0     0     1     1
   1     0     0     0     1
   1     1     0     0     0
   1     1     1     0     0]

A=~b;

Answer 14

[Matt Fig]

One line, anyway. And since the array is at least dynamically pre-allocated, the code is fast.

for ii = 5:-1:1,for jj = min(ii+1,5):-1:max(ii-1,1),A(ii,jj) = 1;end,end

[Jan]

Brr.

[Matt Fig]

LOL Jan. I am surprised that such an answer is faster than both the BSXFUN and EYE + DIAG + DIAG solutions, even for N=1000.

Answer 15

[DGM]

I can't believe that everyone has missed the obvious solution!

rng(46783490); randi([0 1],5,5)

ans = 5×5

1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1

so simple!

[Stephen23]

+1 very nice. What magic did you use to reverse engineer that?

[DGM]

I made use of the classic "commit to brute force and then go to bed" algorithm.

Answer 16

[Paulo Silva]

diag(diag(eye(4,4)),1)+diag(diag(eye(4,4)),-1)+eye(5,5)

or

diag(ones(1,4),1)+diag(ones(1,4),-1)+eye(5,5)

It's similar to the Jan solution above

Answer 17

[marciuc]

Thank you guys...regards from Romania

[Jan]

Please do us the favor and accept one of the answers. Or let your teacher choose one.

Beside the fun, this thread will be really helpful, because it describes the creation of tridiagonal matrices exhaustively.

I really hope you had some fun also.