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Old 12-07-2004, 02:12 PM   #11
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int(xe^(x^2))? that's not so tough.. F(x)=[e^(x^2)]/2

Perhaps you meant int(e^(x^2))?

Anyway, I'm shipping this off to S&S.
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Old 12-07-2004, 02:22 PM   #12
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Quote:
Originally Posted by Godless Wonder
Well, yeah, I know that, but why does it work. Why can you change the problem space like that? It's almost as mysterious as if you transformed the differential equation into a crossword puzzle, solve the crossword puzlle, thinking "well, I don't know how to solve this differential equation, but I have these magic rules to change it into a crossword puzzle, and I know how to do crossword puzzles", then transform the solved crossword puzzle back into the solution of the diff. eq. via some more magic rules. (Ok, not quite that extreme, but almost that mysterious.) I suspect I no longer have the math background necessary to understand even a very good explanation.
The trick is, Laplace is a Linear transform. Addition and scaling are maintained in the mapping--so you can transform the function, then inverse transform it and get the original function back. It's kind of like blowing up the picture in MS-Paint, tweaking it in big scale, and then shrinking it back to the original size.

Any linear transform can be used to solve a differential equation in another space, Fourier, Laplace, etc. but Laplace happens to be real easy in a lot of applications.

Think of it as folding the paper in half when you cut the snowflake. That's a transform.

Ed
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Old 12-07-2004, 04:25 PM   #13
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I think there should be a table in your book that tells what the Laplace and inverse Laplace transforms of various functions and derivatives are. The book usually derives the basic transform and inverse transform formulas by evaluating the integral in the definition. I don't remember the formulas off hand though. I wasn't required to memorize the formulas. They were given on a hand out during the exam.
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Old 12-07-2004, 04:56 PM   #14
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I typed laplace cosine transform into google and I got a suitable result.
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Old 12-07-2004, 05:19 PM   #15
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Originally Posted by Stiletto One
Yeh, our teacher calls it "do the laplace transform, do some algebra, and do the inverse". That's about it.

I doubt I could get my brain around the theory if I tried for a year.
If you're really interested in getting your brain around the theory, take an intro course in topology.

Ed
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Old 12-07-2004, 05:30 PM   #16
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Originally Posted by nermal
If you're really interested in getting your brain around the theory, take an intro course in topology.

Ed
I'm taking an intro course in topology next semester and I can't wait! Topology is one of my favorite mathematics fields.
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Old 12-07-2004, 06:39 PM   #17
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Originally Posted by Demosthenes
I'm taking an intro course in topology next semester and I can't wait! Topology is one of my favorite mathematics fields.
Speaking of which, I just took the final for my intro topology course today. It's definitely interesting stuff if you're looking to think in an even more abstract sense than, say, an introductory analysis course covering basic calculus. I actually was also signed up for such an analysis course this semester and found the two complemented each quite well, at least while we concentrated on metric spaces at the start of topology.

Once we moved on to general topological spaces, it was a shift into more "meta-mathematical" territory. The real-world uses of the general topological space seem less apparent than a metric space, but I can see how they are convenient for proving general results in mathematics. It's not necessarily useful to say, an experimental physicist or an engineer, but I believe theoretical physicists (particularly in string theory and cosmology) rely on it, as well as mathematicians, obviously.

Anyway, good luck with topology next semester and enjoy it! It's good stuff.
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