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Matlab - getinductance

This script demonstrates anonymous functions.

function inductance = getInductance(I, ri, ro1, ro2)

% The function gives back a function to calculate the inducance of a coaxial
% cable depending on distance from the middle of the cable (radius x).
% The function is initialized with its geometry and a steady current.
%
% (c)2010 by Torsten Reuschel, E-Mail: matlabhelp@fuesika.de
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

    inductance = @(x) coax_inductance(x);

    function y = coax_inductance(x)
        if (0 <= x ) && (x <= ri)
            y = 4*pi*1e-7 * I*x / (2*pi*ri^2);
        elseif (ri <= x ) && (x <= ro1)
            y = 4*pi*1e-7 *I /(2*pi*x);
        elseif (ro1 <= x ) && (x <= ro2)
            y = 4*pi*1e-7 * I/(2*pi*x) * (ro2^2-x^2) / (ro2^2-ro1^2);
        else
            y = 0;
        end
    end
end

Notes on using anonymous functions

demonstration of described behaviour (click to enlarge)

When using anonymous functions one should be aware of when and where which information is stored.

Given a matrix A with 10000 by 10000 elements we might want to use an anonymous function that stores this matrix for solving reasons.
Without copying the matrix A we can create more than one function-handle using A.
As soon as we change the content of the matrix A, Matlab makes sure the existing function-handles are still able to use the old matrix.
Matlab will store an copy of the old A - even if the new matrix (or handle) is never used.
If we update the old function-handles, Matlab will clear the old A as soon as no more handle is using it.

This can cause unintentional copying of a serious amount of data.
In case the update is supposed to be available to the function-handles, one should clear the old handles before updating A to keep Matlab from copying the old data.

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Matlab - getinductance

Notes on using anonymous functions