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Anonymous Math Functions in IDL like Matlab [message #75264]

Wed, 23 February 2011 17:47

Ammar Yusuf
Messages: 36
Registered: October 2010

Member

Hi, in Matlab you can do something like:
sqrt = @(x) x.^2;

Is there a way to do this in IDL? I was just wondering.

I tried searching google but that didn't help. Thanks!

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Re: Anonymous Math Functions in IDL like Matlab [message #75310 is a reply to message #75264]

Fri, 25 February 2011 16:50

Ammar Yusuf
Messages: 36
Registered: October 2010

Member

On Feb 25, 11:16 am, Michael Galloy <mgal...@gmail.com> wrote:
> On 2/24/11 8:32 pm, nata wrote:
>
>> I am just curious. What does the expression "sqrt = @(x) x.^2" means ?
>
> It's a lambda function, or anonymous function, a way of specifying a
> function without naming it, i.e., to use inline only once.
>
> For example, see how Python does this:
>
> http://diveintopython.org/power_of_introspection/lambda_func tions.html
>
> Mike
> --www.michaelgalloy.com
> Research Mathematician
> Tech-X Corporation

That's pretty cool. I did not know that.

I know in Matlab what happens is it creates a function say sqrt. In
Matlab
you can then call sqrt(4) and it would return 2.

I found this very helpful instead of making a .m file for each
polynomial function
that I was doing for my homework.

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Re: Anonymous Math Functions in IDL like Matlab [message #75324 is a reply to message #75264]

Fri, 25 February 2011 08:16

Michael Galloy
Messages: 1114
Registered: April 2006

Senior Member

On 2/24/11 8:32 pm, nata wrote:
> I am just curious. What does the expression "sqrt = @(x) x.^2" means ?

It's a lambda function, or anonymous function, a way of specifying a
function without naming it, i.e., to use inline only once.

For example, see how Python does this:

http://diveintopython.org/power_of_introspection/lambda_func tions.html

Mike
--
www.michaelgalloy.com
Research Mathematician
Tech-X Corporation

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Re: Anonymous Math Functions in IDL like Matlab [message #75371 is a reply to message #75310]

Thu, 03 March 2011 15:13

rtk
Messages: 22
Registered: September 2008

Junior Member

I wrote a bunch of higher-order function stuff for IDL awhile back and
included a hack that simulated a lambda function. Basically, it
defined the function on the fly and returned a string with the actual
name. You then used this with the higher-order function (or any
function). So, for your example,

square = lambda('x:x^2')

but to use it directly:

ans = call_function(square, 4)

Outside the context of a higher-order function, this isn't really that
useful. Still, if you want the code, I'll send it, just email me
"oneelkruns" "hotmail" "com". The higher-order functions were DLMs
for Linux and Windows, 32-bit only.

Also, you can define a procedure/function in IDL from the command
line. No need to quit and type a new file:

IDL> .run
- function square, x
- return, x*x
- end
% Compiled module: SQUARE.
IDL> print, square(4)

Perhaps what you are really looking for?

Ron

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