Sequence within a sequence

Hi I want to be able to create a sequence as such

j=1111,2222,3333,4444

It is for use in a loop where j will jump up by 1 for every forth value of i.

thanks

Answer 1

[Wayne King]

Another way (you need Signal Processing Toolbox)

   x = 1:4;
   y = upsample(x,4);
   h = ones(4,1);
   y = filter(h,1,y);

[Daniel Shub]

Hey for once my solution is faster ...

n = 1e7;

m = 10;

tic

x = 1:n;

y = upsample(x,m);

h = ones(m,1);

y = filter(h,1,y);

toc

tic

z = reshape(repmat(1:n, m, 1), n*m, 1);

toc

Elapsed time is 5.215208 seconds.

Elapsed time is 3.261213 seconds.

[Daniel Shub]

Despite my answer being faster (and I think simpler), I like your answer better from a theoretical vantage.

[Wayne King]

:) I don't doubt that at all!

Answer 2

[Daniel Shub]

n = 5;
m = 3;
reshape(repmat(1:n, m, 1), n*m, 1)

Answer 3

[Dr. Seis]

To beat a dead horse...

I thought I remembered a version by Walter using cumsum, but I couldn't find the link. Here's my attempt to recreate:

n = 5;
m = 3;
a = zeros(m,n);
a(1,:) = 1;
b = cumsum(reshape(a,1,numel(a)));

Running Daniel's test, I got ~0.65 seconds and ~1.05 seconds for the reshape&cumsum and repmat&reshape versions, respectively. However, what you save in compute time is eaten up by doing extra typing.

[Daniel Shub]

+1 I knew my answer wouldn't be the fastest. Not only do you have a faster answer, but you also have a faster computer (your answer is faster on my computer also).

Answer 4

[Scott]

excellent that did answer my question however I am trying to use this as a simultaneous loop. My guess is using the parfor command:

function [x]= displacementsi(i,z,nx,ny) m=5 n=3

parfor

    j=reshape(repmat(1:n, m, 1), n*m, 1)
x(1:4)=z((2*i)-(j-2):(2*i)+(j+1))

end end

I get this error

??? Error: File: displacementsi.m Line: 5 Column: 8 Expression or statement is incomplete or incorrect.

Error in ==> fe_test at 112 [x] = displacementsi(i,displacements,nx,ny);

[Daniel Shub]

This is a new question and should be asked as such.

[Scott]

ok sorry