is the logarithmic integral function .

# Details • Mathematical function, suitable for both symbolic and numerical manipulation.
• The logarithmic integral function is defined by , where the principal value of the integral is taken.
• LogIntegral[z] has a branch cut discontinuity in the complex z plane running from to .
• For certain special arguments, LogIntegral automatically evaluates to exact values.
• LogIntegral can be evaluated to arbitrary numerical precision.
• LogIntegral can be used with CenteredInterval objects. »

# Examples

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## Basic Examples(5)

Evaluate numerically:

Plot over a subset of the reals:

Series expansion at the origin:

Series expansions around the branch point at :

Series expansion at Infinity:

## Scope(32)

### Numerical Evaluation(5)

Evaluate numerically to high precision:

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

LogIntegral can take complex number inputs:

Evaluate LogIntegral efficiently at high precision:

LogIntegral can be used with CenteredInterval objects:

### Specific Values(4)

Value at the origin:

Values at infinity:

Find a zero of :

### Visualization(2)

Plot the real part of :

Plot the imaginary part of :

### Function Properties(8)

LogIntegral is defined for all real positive values except 1:

Complex domain:

LogIntegral is not an analytic function:

Has both singularities and discontinuities:

LogIntegral is neither nondecreasing nor nonincreasing:

LogIntegral is neither non-negative nor non-positive:

LogIntegral is neither convex nor concave:

### Differentiation(2)

First derivative:

Higher derivatives:

More integrals:

### Series Expansions(3)

Plot the first three approximations for LogIntegral around :

Series expansions on either side of the branch point at :

LogIntegral can be applied to power series:

### Function Identities and Simplifications(2)

Use FullSimplify to simplify expressions into logarithmic integrals:

### Function Representations(3)

Representation through ExpIntegralEi:

Series representation:

## Applications(4)

Approximate number of primes less than :

Compare with exact counts:

Plot the real part in the complex plane:

Plot the absolute value in the complex plane:

## Properties & Relations(4)

Use FullSimplify to simplify expressions into logarithmic integrals:

Use FunctionExpand to write expressions in logarithmic integrals when possible:

Find the numerical root:

Obtain LogIntegral from integrals and sums:

## Possible Issues(1)

In traditional form, parentheses are needed around the argument:

## Neat Examples(2)

Nested integrals:

Plot the Riemann surface of LogIntegral: