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why there is no definite integral operator in comsol?
Posted 13 giu 2016, 03:58 GMT-4 Parameters, Variables, & Functions 5 Replies
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when I want to calculate a definite integral in comsol, there is no definite integral operator like the int() in the MATLAB. I must use the MATLAB to calculate the numrical solution, and import to comsol.
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Yes, COMSOL can numerically evaluate integrals. You will find these articles helpful:
www.comsol.com/blogs/overview-integration-methods-space-time/
www.comsol.com/blogs/integrate-functions-without-knowing-limits-integral/
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I'm afraid that the examples are not the problem I mentioned.
Now I want define a userdefined function like the attachmennt. The variable s is just for the integral. The variable h is the vaiable used in the model.
Attachments:
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well, if this is just about a space integral or sth. similar, for example for an integration in the results section, one can use a logical step function instead. To bound for example the x value between xmin and xmax one would write in the expressions field something like:
expr*(x<xmax)*(x>xmin)
where expr is the expression you would want to integrate.
Best,
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In response to the message on July 13: The integral that you're describing should be doable by the methods in the previously reference blogs. You may want to contact your COMSOL Support Team if there's a particular example that you're working on here.
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www.comsol.com/blogs/overview-integration-methods-space-time/
But, it would be nice to see more diverse examples, such as how to define functions and intop expressions to integrate in 1D, 2D and 3D, for both definite and indefinite integrals, both over variables that already exist in COMSOL (e.g., x,y), and over user-defined variables or functions (which may themselves be functions of variables like x and y).
In general, the PDF documentation is very short on examples and practical application notes. For example, the explanation of integrate() is limited to explaining in generic terms that the function can take one of two forms:
integrate(expr,var,lower,upper)
integrate(expr,var,lower,upper,to1)
As far as the main user manual goes, that's essentially it. There are some brief comments about the use of coordinate names (which seem to amount to "it doesn't work," without explaining how to make it work) and "spatial at" operators, but not a single worked example.
IMHO, every function should have enough actual examples to show the various ways in which it can be used, and the various syntax that can be used (since there sometimes seem to be extensions that are not evident from the generic descriptions).