# ProductLog

ProductLog[z]

gives the principal solution for w in .

ProductLog[k,z]

gives the k solution.

# Details

• Mathematical function, suitable for both symbolic and numerical manipulation.
• The solutions are ordered according to their imaginary parts.
• For , ProductLog[z] is real.
• ProductLog[z] satisfies the differential equation .
• For certain special arguments, ProductLog automatically evaluates to exact values.
• ProductLog can be evaluated to arbitrary numerical precision.
• ProductLog automatically threads over lists.
• ProductLog[z] has a branch cut discontinuity in the complex z plane running from to .
• ProductLog[k,z] allows k to be any integer, with corresponding to the principal solution.
• ProductLog[k,z] for integer has a branch cut discontinuity from to 0.
• ProductLog can be used with Interval and CenteredInterval objects. »

# Examples

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## Basic Examples(6)

Evaluate numerically:

Plot over a subset of the reals:

Plot over a subset of the complexes:

Series expansion at the origin:

Asymptotic expansions at Infinity:

Asymptotic expansions at a singular point:

## Scope(36)

### Numerical Evaluation(6)

Evaluate numerically:

Evaluate to high precision:

The precision of the output tracks the precision of the input:

Complex number input:

Evaluate efficiently at high precision:

ProductLog threads elementwise over lists and matrices:

ProductLog can be used with Interval and CenteredInterval objects:

### Specific Values(4)

Values of ProductLog at fixed points:

Values at zero:

Values at infinity:

Find a value of x for which the ProductLog[x]=0.5 using FindRoot:

### Visualization(3)

Plot the ProductLog function:

Plot the real part of :

Plot the imaginary part of :

Polar plot with :

### Function Properties(10)

ProductLog is defined for all real values from the interval [-,):

ProductLog is defined for all complex values:

The two-argument form requires that be an integer and :

The real range:

ProductLog is not an analytic function:

Nor is it meromorphic:

ProductLog is increasing on its real domain:

ProductLog is injective:

ProductLog is not surjective:

ProductLog is neither non-negative nor non-positive:

ProductLog has both singularity and discontinuity in (-,-]:

ProductLog is concave on its real domain:

### Differentiation(3)

The first derivative with respect to z:

Higher derivatives with respect to z:

Plot the higher derivatives with respect to z:

Derivative of a nested logarithmic function:

### Integration(3)

Compute the indefinite integral using Integrate:

Verify the anti-derivative:

Definite integral of ProductLog:

More integrals:

### Series Expansions(5)

Find the Taylor expansions using Series:

Plots of the first three approximations around :

Expand the two-argument form:

The general term in the series expansion using SeriesCoefficient:

Find the series expansion at Infinity:

Find series expansions at branch points and branch cuts:

The series expansion at infinity contains nested logarithms:

### Function Identities and Simplifications(2)

ProductLog gives the solution for the following equation:

Expand assuming real variables x and y:

## Generalizations & Extensions(3)

Evaluate numerically on different sheets of the Riemann surface:

Find series expansions at branch points and branch cuts:

The branch points and branch cuts are different for :

## Applications(9)

Solve an equation in terms of ProductLog:

Plot the real and imaginary parts of ProductLog:

Plot the Riemann surface of ProductLog:

Calculate the limit of :

Compare the exact result with explicit iterations for :

Determine the number of labeled unrooted trees from the generating function:

Solve LotkaVolterra equations:

Find the frequency of the maximum of the blackbody spectrum:

Solve the Haissinski equation:

Equipotential curves of a plate capacitor:

## Properties & Relations(5)

Compositions with the inverse function may need PowerExpand:

Use FullSimplify to simplify expressions containing ProductLog:

Solve a transcendental equation:

Integrals:

## Possible Issues(2)

Generically :

On branch cuts, machineprecision inputs can give numerically wrong answers:

Use arbitraryprecision arithmetic to get correct results:

## Neat Examples(2)

Nested derivatives:

Nested integrals:

Wolfram Research (1996), ProductLog, Wolfram Language function, https://reference.wolfram.com/language/ref/ProductLog.html (updated 2022).

#### Text

Wolfram Research (1996), ProductLog, Wolfram Language function, https://reference.wolfram.com/language/ref/ProductLog.html (updated 2022).

#### CMS

Wolfram Language. 1996. "ProductLog." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2022. https://reference.wolfram.com/language/ref/ProductLog.html.

#### APA

Wolfram Language. (1996). ProductLog. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ProductLog.html

#### BibTeX

@misc{reference.wolfram_2022_productlog, author="Wolfram Research", title="{ProductLog}", year="2022", howpublished="\url{https://reference.wolfram.com/language/ref/ProductLog.html}", note=[Accessed: 01-June-2023 ]}

#### BibLaTeX

@online{reference.wolfram_2022_productlog, organization={Wolfram Research}, title={ProductLog}, year={2022}, url={https://reference.wolfram.com/language/ref/ProductLog.html}, note=[Accessed: 01-June-2023 ]}