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Dec 12, 2018
07:45 AM

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Dec 12, 2018
07:45 AM

ODE solver

Hey guys I want to ask,

When I have two derivation dCOl/dx and dCOg/dx, there are two ways to use ODE solver :

First by solving it in 1 term (so its coupled) or second by solving one of each first.

I tried it and it gives a different result, now i'm wondering what is actually the difference when I do derivation coupled and uncoupled.

Thanks

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6 REPLIES 6

Dec 12, 2018
08:03 AM

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Dec 12, 2018
08:03 AM

The possible ways of solution should not matter:

- If COg depends on COl or vice versa, you (generally) CANNOT solve one without the other.

You might be able to express one coompletely in terms of the other, that leaves you with one expression for Odesolve. Otherwise you should feed a set of equations to Odesolve.

- If COg and COl are completely independend, you have the option to solve them separately, or combine them in a set of equations that Odesolve should be able to solve.

Success!

Luc

Dec 12, 2018
09:09 AM

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Dec 12, 2018
09:09 AM

You have coupled equations, where the value of one is required in the expression for the other. They must be solved together. If you solve only one the value of the other is fixed and therefore gives the wrong result for the solution.

Dec 12, 2018
12:21 PM

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Dec 12, 2018
12:21 PM

Why don't you post your worksheet so that we can see what kind of ODEs your are dealing with and (most important) if they are independent from each other or not.

If they are not independent you can't solve them singly, of course.

Dec 12, 2018
03:18 PM

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Dec 12, 2018
03:18 PM

The OP did post worksheets, under different names, with different topics:

https://community.ptc.com/t5/PTC-Mathcad/Help-for-iteration/m-p/584832#M183746

https://community.ptc.com/t5/PTC-Mathcad/Integration-Solver/m-p/578494#M183033

Luc

Dec 12, 2018
05:07 PM

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Dec 12, 2018
05:07 PM

@LucMeekes wrote:

The OP did post worksheets, under different names, with different topics:

That may be, but to get an answer in THIS thread he should post his sheet in THIS thread and the sheet should fit his question for dCOl/dx and dCOg/dx

Furthermore the sheet should show his attempts and different results when solving singly and as a system.

In the other threads he was asking for a method of iteration while in fact it looks he was just after a system of ODEs which he already had solved in his sheet.

The question should be concentrated in ONE thread and a mod should then delete his other posts to avoid further confusion.

Dec 12, 2018
05:24 PM

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Dec 12, 2018
05:24 PM

I couldn't agree with that more...

Luc