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if condition in variable definitions
Posted 2011年4月12日 GMT-4 10:36 Parameters, Variables, & Functions Version 4.1 6 Replies
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I was wondering how to implement if conditions in variable definitions?
For example, if I wanted to define a variable a, and it is based on a condition of b, which has been defined as another variable.
a = 1 if b>0
a = 3 if b<=0
I was wondering how to implement this?
And another situation is, I have already defined a variable M, then another variable depends on M:
c = M^2 + 5 when M<0.5
c = 2*M/(M+1)^2 when M>=0.5
Could anyone please help with this? Thanks a lot in advance!
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you can multiply boolean expressions:
3*(b<=0) + 1*(b>0) behaves as desired for a.
The expression for c would then be:
(M^2 + 5)*(M<0.5) + (2*M/(M+1)^2)*(M>=0.5)
Cheers
Edgar
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I have a question in connection with this.
I wish to add a boolien expression, which should use time variable. I want to know, how the time is accessed? What is the variable name?
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I think the time variable is always "t".
Cheers
Edgar
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The time in COMSOL is "t" (in seconds) but it is not formally declared before you call a transient solver, therefore when you mix stationary followed by a time series and you want to debug such a solution with variables depending on "t" these might flag an error.
To avoid this, add a "Parameter" t = 0[s], this will be overwritten by COMSOL once the time solver comes up
Sometimes it is better to use a value slightly different from "0" to avoid all =0 in your variables, this is all model and case dependent ;)
--
Good luck
Ivar
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Thanks to both of you!
Dhanashri.
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