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variable determined by integral formula

Posted Feb 13, 2014, 4:36 p.m. EST Materials, Parameters, Variables, & Functions Version 4.3b 2 Replies

Terence Dong
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Normally when people talk about integration, they refer to coulpling variables, which could be integrated over space or time.

In my variable definition, I have a variable determined by a integral formula.
For example, one varialble is the integration of f(r) over r with up and low limits, r can be particle size or whatever, other than space coordinates or time.
I tried to search from the website for information, but still have no idea to figure this problem out.

This qustion was also posed by others 1 year ago. Please refer to:
www.comsol.com/community/forums/general/thread/28492/

Could someone give me some nice advices? I will appreaciate a lot for your answer!
2 Replies Last Post Mar 31, 2014, 11:14 a.m. EDT
Daniel Smith COMSOL Employee

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Posted: 1 decade ago Feb 13, 2014, 5:33 p.m. EST
Dear Terence, you can use the integrate() function, as described on P230 of the COMSOL Multiphysics Reference manual (in the V4.3b documentation):

integrate(expr, var, lower, upper) computes the integral of expr for the integration variable var over an interval specified by expressions lower for the lower limit and upper for the upper limit. The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values.

Dan
Dear Terence, you can use the integrate() function, as described on P230 of the COMSOL Multiphysics Reference manual (in the V4.3b documentation): integrate(expr, var, lower, upper) computes the integral of expr for the integration variable var over an interval specified by expressions lower for the lower limit and upper for the upper limit. The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. Dan
Paramita Chatterjee
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Posted: 1 decade ago Mar 31, 2014, 11:14 a.m. EDT
Hello,
I am using Comsol 4.3b. I arrived in a problem. Could you please help me. The problem is,
u'=\int_{0}^{t}(-u)ds, u(0)=1 , u'(0)=0, which implies u(t)=cost. Now I want to see the value of cos1.
I choose coefficient form of PDE (time dependent) .
Thanking you.
Best regards.
- Paramita Chatterjee
Hello, I am using Comsol 4.3b. I arrived in a problem. Could you please help me. The problem is, u'=\int_{0}^{t}(-u)ds, u(0)=1 , u'(0)=0, which implies u(t)=cost. Now I want to see the value of cos1. I choose coefficient form of PDE (time dependent) . Thanking you. Best regards. - Paramita Chatterjee

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