Introduction to the Lambert W Function

In this video I introduce the Lambert W Function, and work to demystify it, as well as work through a few simple algebraic examples using it.
For videos on how this connects to Wien's law, visit:
• Wien's Law

[@full_legit191]

KZbin is lacking of this kind of content thanks you for sharing it

[@physicsandmathlectures3289]

Glad you found it useful!

[@__hannibaal__]

Just see how much view only 1000; these our World; it became silly Thanks for video

[@IkumieIkupi]

True

[@jackingham3069]

"I'll circle this cos I like circling stuff..." *Draws a square around it" :-D Great lecture! Thank you!

[@physicsandmathlectures3289]

Haha, I'm glad you found it both useful and amusing!

[@johnmartinez2445]

probably the sexiest explanation of the Lambert W function and its application. I don't usually comment, but you have done me such a service that I needed to comment!

[@KittysCat-j7x]

So you still need a computer to evaluate the result and get a value? Every video I've seen on this function talks about the nice property, but conveniently neglects how one goes about evaluating the Lambert W function. So, we haven't really solved a problem here. We have just manipulated the equation and changed its form. It's not much different than saying "The solution to this equation is that answer that solves the equation."

[@physicsandmathlectures3289]

In a sense I completely agree with you. Most special functions are defined to be the answer that solves some equation. But this doesn't mean that they aren't useful. Take a function like sine or cosine. One way of defining them is as the solution to the differential equation y''(x) = y(x). But in spite of this definition it is often more useful to work in terms of sine and cosine instead of leaving a problem otherwise unsimplified. In this case it's the ability to manipulate a problem more easily using the special function that makes it useful. In the case of the Lambert W function, it is nice to be able to write an exact function that is the inverse of xe^x, rather than working with an implicit form of the problem. Additionally, seeing the special function explicitly makes it easier to see and use the properties of the special function. I would also say that the process of evaluating the W function is comparable to evaluating a function like sine or cosine. What is sin(.2)? The way we find out is by plugging .2 into the Taylor series for sine and if we're working by hand then we evaluate a few terms and pay attention to the error. If we're on a computer then we just plug it in and get a very good answer. Likewise, there is a series for the Lambert W function (see my other videos), as well as other representations using integrals and continued fractions that one can use to get arbitrarily accurate values of the function. These can be approximated by hand, or you can just use a computer to get an exact answer. Thank you for the question. I hope my response makes some sense.

[@Vnifit]

@@physicsandmathlectures3289 This is a great answer!

[@nicholasleclerc1583]

@@physicsandmathlectures3289 Woops, forgot a minus sign (-) in your implicit definition of (co)sinusoidal wave functions

[@preetib6819]

You can use newtons method to approximate W function

[@ilyafoskin]

It’s the same for many functions that we’re all so familiar with that we’ve forgotten how unsatisfying they are as solutions. We all have the log function on our calculators but we don’t realise that using the log function to solve equations was only possible before calculators because people created massive tables of numerical approximations for different input values. They would say the solution is log(2), then go look that up in a table. The W function operates the exact same way. If the Lambert W function was on our calculators, it would become as recognisably intuitive as the log.

[@alphamega3306]

Great explanation. I like how you make sense of it, rather than just throwing out a bunch of definitions. Also, it would be very useful if a link to the next video were in the description.

[@wilsonjp23]

Dude... an amazing explanation. 2 mins into the video and I subbed!

[@jamesmccamish3901]

Fantastic introduction, very helpful to me. Thank you.

[@robertkeyling3131]

I like it ❤ Origin of this topic is so called calculus, almost nobody knows.

[@laman8914]

I am not a mathematician but I have watched a number of clips explaining the Lambert W Function. What I understood is that if one has an exponential function and one cannot solve it, one might resort to defining its inverse function. This means resorting to the Lambert (W) expression of that function, on the condition that the Lambert (W) is not defined for values smaller than minus (1/e). I hope I have expressed it properly. If not, please advise, correct so I can understand this properly.

[@alijoueizadeh2896]

Thank you for your precious time.

[@donlimonesioyt9644]

I aproached this function in a very curious way. I was trying to determine in which intervals the function f(x)=xlnx-1 was positive or negative, thus having to calculate the value of x for f(x)=0. I tried to use the propierties of logarithms, but I was stuck in a cycle and didn’t manage to solve the equation. Then I tried to draw the graphic of the function and it seemed to cross with the x axis in somewhere near 1,73. I started substituting with the calculator values near that number and manage to get an aproximation of x. However, I still thought that there should be a way to get the exact value. I didn’t know what to do next, so, I asked, chat gpt, and it told me about the Lambert function. And that’s basically how I got to this video.

[@fizisistguy]

Well but the inverse functions such as square root give us an intuitive sense as you can perform them on simple numbers like 4, 9 and 36. What does the lambert W function do to numbers? Like how do we even calculate values attained from it?

[@mixcher849]

This video is just great

[@physicsandmathlectures3289]

Thank you!

[@okayedokaylad]

Best explanation!

[@glennglazier4046]

But what is the NUMERICAL value of W(7)???

[@JM-cv7nv]

About 1.525

[@marcosohanian4964]

Amazing video! Thxx

[@AzharLatif-d4z]

Longed to see an integer, decimal value, or complex number on the unit circle of Lambert W Function. So far am disappointed, and confused about the real use of Lambert W Function. Why no one has tabulated, to look up the values of Lambert W Function, live happily ever after? So far videos of Lambert W Function are hot air.

[@That_One_Guy...]

Is there any elementary representation of this function ? (Like how trig functions can be expressed in exponential function)

[@physicsandmathlectures3289]

I don't think so. There are plenty of other representations using integrals or continued fractions, but I'm not aware of any elementary function representation.

[@pixerhp]

No actually, I don’t believe this one’s non-elementary.

[@santerisatama5409]

@@physicsandmathlectures3289 Hm. Continued fractions (especially in Stern-Brocot type binary tree structures) are elementary in terms of proof theory. Not sure whether they can be called functions, though.

[@Alrukitaf]

Very useful vid. But my brain hurts.

[@UnsocialExperiment]

Where do rainbows come from, how does the positraction on a Plymouth work, how does a Lambert W function work? It just does.

[@renesperb]

The equation in the title does not make much sense if you want to define the Lambert function.Why not write yExp[y] = x ,then y = W[x] ?

[@kyks6771]

I want a Teflon transformation function asap 💩

[@raf.4028]

whered ya go

[@physicsandmathlectures3289]

Coursework has had me busy these last few months. I'm hoping to start posting semi-regularly within the next few weeks though.

[@AaryanJain-lk3jt]

Am I missing something? This doesn't actually explain what the lambert function specifically does to find the value of the variable, instead just re-formats it

[@jerryhopfe5111]

There is no easy way to find the number , but that's also true for the natural logarithm , etc. C'est la vie ...

[@marcelverhoeven3514]

How to calculate the exact value (Example in Thonny) from scipy.special import lambertw import numpy as np # Calculate W(-5 * e^(-7)) using the branch W_{-1} z = -5 * np.exp(-7) w_value = lambertw(z, k=-1).real # Using the W_{-1} branch # Calculate x = W(-5 * e^(-7)) + 7 x = w_value + 7 print(f"The value of x is: {x}")

[@kaydenlimpert2779]

log_e(x) is the inverse of e^x, not log(x), because log(x) is the same as log_10(x)

[@iancorbett7457]

Log(x) can represent any base, in algebra it’s commonly used to refer to base 10 but in higher math it’s not uncommon to use it for other bases

[@kaydenlimpert2779]

@@iancorbett7457 ok

[@AshrafAli-qn3gb]

😊👌

[@izzyqrz1]

This looks DEQ stuff a little

[@pel6664]

You need to practice how to text on the board before talking

[@pianotalent]

Boring explanation...with too many unnecessary details...

[@neuralwarp]

Please don't whistle into the microphone.

[@Cmrboy26]

🤓