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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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How do I write three functions to one in comsol?

Posted 2013年7月20日 GMT-4 22:14 Low-Frequency Electromagnetics Version 4.3b 2 Replies

Xin Wei
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Excuse me. I want to ask a question. when 0=<t<=1, the function is f(t). When 1<t<=2, the function is g(t). When 2<t<=3, the function is h(t). How can the three functions be written one? I write "f(t)*(t>=0&t<=1)+g(t)*(t>1&t<=2)+h(t)*(t>2&t<=3)", but it is wrong. What shoud I do?

Best your wishes,

Xin Wei
2 Replies Last Post 2013年7月21日 GMT-4 19:01
Suresh Seetharam
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Posted: 1 decade ago 2013年7月21日 GMT-4 14:27
Hi,


What do you mean by wrong, what happens? Did you try replacing & with &&.


Suresh
Hi, What do you mean by wrong, what happens? Did you try replacing & with &&. Suresh
Adam Kessler
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Posted: 1 decade ago 2013年7月21日 GMT-4 19:01
I have found that the *(t>1) or *(c>0) etc operators can be a little bit unreliable in some models. I have had more success with if statements. So for your function, that could be written as

F(t) = if(t>1, if(t>2, h(t), g(t)), f(t))

If you have additional values of t outside of the range [0,3] then you may need an extra if loop to close these.

I know this is a little inefficient, but I have run both time- and concentration-dependent functions in the past, and found that this is a more reliable method.
I have found that the *(t>1) or *(c>0) etc operators can be a little bit unreliable in some models. I have had more success with if statements. So for your function, that could be written as F(t) = if(t>1, if(t>2, h(t), g(t)), f(t)) If you have additional values of t outside of the range [0,3] then you may need an extra if loop to close these. I know this is a little inefficient, but I have run both time- and concentration-dependent functions in the past, and found that this is a more reliable method.

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