KroneckerDelta in matlab

Question

This link shows that there is a kronecker delta function in matlab. However:

>> help kroneckerDelta

    kroneckerDelta not found

I am using R2011b, so maybe this wasn't programmed into the toolkit yet?

EDIT:: It works in MuPad, just not in matlab...

.

Also for future reference, you would have to check your version documentation as you may note that link provides R2013a documentation (so do all searches). So try from the Mathworks >> Support >> Documentation Center >> Other Release. — voxeloctree, Jul 18 '13 at 20:01

score 4 · Answer 1 · edited May 10 '16 at 07:16

4

The Kronecker delta returns 1 if j==k...

So you could simplify the expression with:

function d=kronDel(j,k)

d=j==k

end

Luckily, MATLAB represents booleans as (0,1)

edited May 10 '16 at 07:16

Christopher Creutzig

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answered Jul 18 '13 at 20:31

user2293601

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You should format your code. Also, this question is tagged [matlab], not [octave], so `end` should be used. It would probably also be a good idea to cast the output to `double` or the class of the input variables. – horchler Jan 29 '15 at 16:15

voxeloctree · Accepted Answer · 2013-07-18T19:56:57.703

2

I don't see it in my R2012b so perhaps not. Unless you need the symbolic math, you could always write your own. Something as simple as

function d = kronDel(j,k)

if j == k
    d = 1;
else
    d = 0;
end

edited Jul 18 '13 at 19:56

answered Jul 18 '13 at 19:44

voxeloctree

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Peeter Joot · Answer 3 · 2015-03-24T19:55:07.220

2

You can also do this inline, like

( a == b )

However, using an anonymous function is a nice way to convert a one liner like this into something that is more readable

kronDel = @(j, k) j==k ;

kronDel( 2, 1 )
kronDel( 2, 2 )

edited Mar 24 '15 at 19:55

answered Dec 08 '14 at 14:59

Peeter Joot

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score 0 · Answer 4 · answered Jul 18 '13 at 23:14

Your link to is to the MuPAD function kroneckerDelta -note the URL and the funky typography of the examples. You won't see it in any version of Matlab because it's only available through MuPAD (type mupad in your command window and try in the window that launches). I have no idea when it was added to MuPAD, I know that it's at least in R2012b. You may have it even if the help command returns nothing.

If you have kroneckerDelta in R2011b, you won't be able to run it from the regular command window or Editor in the normal fashion.

evalin(symengine,'kroneckerDelta(1,1)')

or the more flexible

feval(symengine,'kroneckerDelta',1,1)

See more here. However, if you're not working with symbolic math, there's really no reason to use this function that I can see -it's not even vectorized! I'd go with a solution that fully emulates kroneckerDelta's behavior in double precision:

function d=kronDel(m,n)
if nargin == 1
    d = double(m==0);
else
    d = double(m==n);
end

...just saw your edit about it working in MuPAD. Well, here's the rest of the story... — horchler, Jul 18 '13 at 23:15

KroneckerDelta in matlab

4 Answers4

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