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Can COMSOL call an external function ?function in Matlab?

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In the subdomain setting, can I specify certain property with an expression of a Matlab function.

for example, if I specify this property to be '1*(x<0.5)+2*(x>=0.5)', it works.
while, if I set it to be 'fx', and fx is a function defined in Matlab as
function y=fx(x)
if x<0.5
y=1
else
y=2
end
end
it doesn't work.

Does it mean COMSOL cannot call an external Matlab function in modeling setting? or did I do it in a wrong way?
For my real case, the expression I would use cannot be written in an analytical way, so the user-defined function in COMSOL seems not work for me... Does anybody have the answer or any alternative methods for my problem?
Thanks!

8 Replies Last Post 11.11.2010, 08:13 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 13.01.2010, 14:54 GMT-5
Hi

indeed, from my understanding too, COMSOL cannot call a matlab function, but it can call a COMSOL function, but you have less freedom to elaborate what you will therein.

This is improved in the to come V4, will have to wait and see, and learn again ...

Ivar
Hi indeed, from my understanding too, COMSOL cannot call a matlab function, but it can call a COMSOL function, but you have less freedom to elaborate what you will therein. This is improved in the to come V4, will have to wait and see, and learn again ... Ivar

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Posted: 1 decade ago 13.01.2010, 15:15 GMT-5
well from having read the documentation section "using matlab functions" it could [ I dont have matlab currently so no practical experience tough..] but from my prior experience with matlab you have to be careful that the special function you define is in a path matlab knows
[ can you call the function from within the matlab window..? and get an answer then...
well from having read the documentation section "using matlab functions" it could [ I dont have matlab currently so no practical experience tough..] but from my prior experience with matlab you have to be careful that the special function you define is in a path matlab knows [ can you call the function from within the matlab window..? and get an answer then...

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 13.01.2010, 16:14 GMT-5
Hi
Matlab and Comsol are close, so you run one from the other, both ways, but mainly comsol from matlab for any secial function or application. but from V4 (to come) I beleive you can do far more without bothe on your PC, just with COMSOL i mean. Have to wait to see.

Good luck
Ivar
Hi Matlab and Comsol are close, so you run one from the other, both ways, but mainly comsol from matlab for any secial function or application. but from V4 (to come) I beleive you can do far more without bothe on your PC, just with COMSOL i mean. Have to wait to see. Good luck Ivar

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Posted: 1 decade ago 13.01.2010, 16:49 GMT-5

In the subdomain setting, can I specify certain property with an expression of a Matlab function.

for example, if I specify this property to be '1*(x<0.5)+2*(x>=0.5)', it works.
while, if I set it to be 'fx', and fx is a function defined in Matlab as
function y=fx(x)
if x<0.5
y=1
else
y=2
end
end
it doesn't work.

Does it mean COMSOL cannot call an external Matlab function in modeling setting? or did I do it in a wrong way?
For my real case, the expression I would use cannot be written in an analytical way, so the user-defined function in COMSOL seems not work for me... Does anybody have the answer or any alternative methods for my problem?
Thanks!


The first example you gave above was in inline function, whereas the second one was not. Also, to invoke matlab you need to have it running in client/server mode along with comsol, and your function paths specified, else comsol doesn't know where to look to find the code. Finally, if all else fails you can export your application to matlab, at which point it becomes a matlab program and you can embed whatever additional matlab code you want.
[QUOTE] In the subdomain setting, can I specify certain property with an expression of a Matlab function. for example, if I specify this property to be '1*(x=0.5)', it works. while, if I set it to be 'fx', and fx is a function defined in Matlab as function y=fx(x) if x

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Posted: 1 decade ago 15.01.2010, 15:09 GMT-5
I was just running it under Matlab. Here is my code for a test sample:

fem.geom=rect2(1, 0.1);
clear appl
appl.mode='ConductiveMediaDC';
%appl.equ.sigma='1e7*(y<0.05)+1e8*(y>=0.05)';
appl.equ.sigma='fy(y)';
appl.bnd.V0={0, 30, 0};
appl.bnd.type={'V0', 'V', 'nJ0'};
appl.bnd.ind=[3, 1, 3, 2];
fem.appl=appl;
fem=multiphysics(fem);
fem.mesh=meshinit(fem);
fem.xmesh=meshextend(fem);
fem.sol=femstatic(fem);

where fy(y) is a function defined in matlab and saved under the same directory where I ran the code.

function sigma=fy(y)
sigma=1e7;
end

But, it didn't work, and reported an "error in external function..."


well from having read the documentation section "using matlab functions" it could [ I dont have matlab currently so no practical experience tough..] but from my prior experience with matlab you have to be careful that the special function you define is in a path matlab knows
[ can you call the function from within the matlab window..? and get an answer then...


I was just running it under Matlab. Here is my code for a test sample: fem.geom=rect2(1, 0.1); clear appl appl.mode='ConductiveMediaDC'; %appl.equ.sigma='1e7*(y=0.05)'; appl.equ.sigma='fy(y)'; appl.bnd.V0={0, 30, 0}; appl.bnd.type={'V0', 'V', 'nJ0'}; appl.bnd.ind=[3, 1, 3, 2]; fem.appl=appl; fem=multiphysics(fem); fem.mesh=meshinit(fem); fem.xmesh=meshextend(fem); fem.sol=femstatic(fem); where fy(y) is a function defined in matlab and saved under the same directory where I ran the code. function sigma=fy(y) sigma=1e7; end But, it didn't work, and reported an "error in external function..." [QUOTE] well from having read the documentation section "using matlab functions" it could [ I dont have matlab currently so no practical experience tough..] but from my prior experience with matlab you have to be careful that the special function you define is in a path matlab knows [ can you call the function from within the matlab window..? and get an answer then... [/QUOTE]

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Posted: 1 decade ago 10.11.2010, 18:14 GMT-5
Ou,
i am curious to know if you resolved the issue with the latest COMSOL40a? if so can you share, i am interested in the same issue.

--
merci
Ou, i am curious to know if you resolved the issue with the latest COMSOL40a? if so can you share, i am interested in the same issue. -- merci

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Posted: 1 decade ago 10.11.2010, 18:17 GMT-5
Hello Ivar,
please did you find out if this can be done in COMSOL40a? if so, please can you share the knowlegde.

in the meantime i will be comsoling :)

--
merci
Hello Ivar, please did you find out if this can be done in COMSOL40a? if so, please can you share the knowlegde. in the meantime i will be comsoling :) -- merci

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 11.11.2010, 08:13 GMT-5
Hi

so far I have managed to survive without calling matlab vit 4.0 and 4.1 now, so sorry I cannot telll.

the only thing I know for sure is that your matlab function must be vector input compatible

--
Good luck
Ivar
Hi so far I have managed to survive without calling matlab vit 4.0 and 4.1 now, so sorry I cannot telll. the only thing I know for sure is that your matlab function must be vector input compatible -- Good luck Ivar

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