Reverse vector in matlab

Hi all,

I have a vector z=0:dz:h, which I want to reverse so I get z*=h:dz:0.

For example if

h=5 and dz=1, then z=0 1 2 3 4 5

I want to obtain z=5 4 3 2 1

Does anyone know a smart way to achieve this in Matlab?

Thanks!

[James Tursa]

Do you want the 0 on the end? I.e., is your 5 4 3 2 1 a typo and you really mean 5 4 3 2 1 0?

[Ellen]

Sorry, it is a typo indeed! Thanks!

Answer 1

[James Tursa]

z = fliplr(z);

or

z = h:-dz:0;

[Jan]

Inlining fliplr reduces the overhead of calling a function:

z = z(numel(z):-1:1);

[Jos (10584)]

but ... numel is also a function. Another option:

z = z(end:-1:1)

[José-Luis]

Just to be thorougly anal, end is a function as well. Just try

 edit end

[Jan]

end is significantly slower than a length command. In addition I've seen so many bugs related to end in Matlab's bug-reports, that I avoid it even in the trivial cases.

function mySillyTest
x = rand(1, 1000);

tic;
for i = 1:1e6
  c = x(end);
end
toc

tic;
for i = 1:1e6
  c = x(numel(x));
end
toc

% Matlab 2009a/64, Win7, Core2Duo
Elapsed time is 0.016512 seconds.
Elapsed time is 0.005833 seconds.

% R2011b:
Elapsed time is 0.014812 seconds.
Elapsed time is 0.005928 seconds.

But: "significantly" faster for this tiny detail does usually not mean, that the total time of a program will be effected significantly.

[Jos (10584)]

Just to extra-thoroughly anal, I never said that end is not a function ;-)

I concur with Jan's opinion about the use of end ...