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I solved a differential equation some time ago and I need to solve for $y$. How can we solve for $y$ using the Lambert W function?

$C_1+x = e^y+Cy$

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    @hhh Infinite loop!2012-02-21

1 Answers 1

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Hint

$\large C^{-1}\exp\left(C^{-1}e^y+y\right)=(C^{-1} e^y)e^{(C^{-1} e^y)} $

Answer

$\hskip 2in \displaystyle \begin{array}{} A+x=e^y+Cy \\ \frac{A+x}{C}=\frac{e^y}{C}+y \\ \frac{1}{C}\exp\left(\frac{A+x}{C}\right)=\frac{e^y}{C}\exp\left(\frac{e^y}{C}\right) \\ W\left(\frac{1}{C}e^{(A+x)/C}\right)=\frac{e^y}{C} \\ y=\log\left[ C\; W\left(\frac{1}{C}e^{(A+x)/C}\right)\right] \end{array}$

Note also that $\log W(z)=\log z-W(z)$, if you want to compare with what W|A gives.

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    Thanks. I mostly use MathType's "translator" to code my equations, but I know a little of LaTeX so I think I can manage.2012-02-20