How do I generate a given Matrix in one command?
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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
4 个评论
Jan
2011-2-23
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
2011-2-23
For clarification: Does "I give you a beer" belong to the list of helpful commands or is this a different topic?
Paulo Silva
2011-2-24
+1 vote to marciuc just because of the beer :)
Jan
2011-2-25
+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.
回答（17 个）
Jan
2011-2-23
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.
Sean de Wolski
2011-2-23
Probably the most compact:
A = toeplitz([1 1 0 0 0])
1 个评论
Jan
2011-2-23
This is the most compact command, except for the ambitious RAND apporach. I vote it.
Jan
2011-2-23
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.
5 个评论
Matt Fig
2011-2-23
Always a sense of humor.
Andrew Newell
2011-2-23
A = randint(5) would be a shorter way of maybe getting the right answer!
Jan
2011-2-23
You need the Communications Toolbox for RANDINT.
Andrew Newell
2011-2-23
A small price to pay for elegance!
Jiro Doke
2011-2-23
Or if you have MATLAB R2008b or newer,
A = randi([0 1], 5)
Jan
2011-2-23
A = dec2bin([24 28 14 7 3]) - '0'
4 个评论
Jiro Doke
2011-2-23
+1 vote!
Matt Tearle
2011-2-24
That is sick, wrong, disturbing, and I love it
David Young
2011-2-24
dec2bin('vzlea'-'^')-'0'
Jan
2011-2-24
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.
Matt Tearle
2011-2-23
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)
1 个评论
Sean de Wolski
2011-2-23
Nice job with your current favorite!
Kenneth Eaton
2011-2-28
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)));
1 个评论
Jan
2011-2-28
*You* have suggested it now. So I can't believe it now, too. +1
Jan
2011-2-23
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.
2 个评论
Sean de Wolski
2011-2-23
Can I have your beer ?!
Matt Tearle
2011-2-23
You can have all the beer that marciuc's teacher sends me. How's that for a deal?
Paulo Silva
2011-2-23
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
1 个评论
Sean de Wolski
2011-2-23
Yay! The infinite monkey makes its second appearance in a week.
Walter Roberson
2011-2-25
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)))
1 个评论
Jan
2011-2-25
Thanks for line breaking. This solution will drive marciuc's teacher crazy. Such ugly! +1
Jan
2011-2-23
A = abs(bsxfun(@minus, 1:5, transpose(1:5))) < 2
Jan
2011-2-23
A = 1 - (tril(ones(5), -2) + triu(ones(5), 2))
Jan
2011-2-24
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.
Paulo Silva
2011-2-24
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;
Matt Fig
2011-2-24
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
Paulo Silva
2011-2-23
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
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