### Author Topic: integrating factor  (Read 1357 times)

#### Blair Zhang

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##### integrating factor
« on: November 20, 2018, 03:15:56 PM »
How to derive the integrating factor for function only depends on x?

#### wuyuning

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##### Re: integrating factor
« Reply #1 on: November 20, 2018, 03:22:19 PM »
Here is one way to prove it.

We need to find a factor so that make the ODE become exact.
So μ(x, y)M(x, y) + μ(x, y)N(x, y)y = 0, if the equation is exact, then (μM)y = (μN)x.
Further more, Mμy − Nμx + (My − Nx)μ = 0. You are asking about integrating factor only depends on x, so it is safe to assume that μy = 0(taking derivative with respect to y).  then we find that dμ/dx= μ(My − Nx)/N. If (My − Nx)/N is a function of x only, then there is an integrating factor μ that also depends only on x.

I hope this brief explanation helps.