# lambertW

LambertW-func

## Definition:

The **lambertW(***x*, *branch*, *offset*) function calculates an approximate value for the real branches of Lambert’s W function
(sometimes known as the ‘product log’ or ‘Omega’ function), which is the inverse function of

for

The function f is many-to-one, and so, except at 0, W is multivalued.

This labtalk function is implemented from NAG9(c05bac), you may refer to detailed information in the NAG library.

## Parameters:

- x
- the value if offset is not chosen, or the offset from of the intended argument to W if the offset is chosen.
- branch
- the real branch required, should be 0 or -1.
- offset
- controls whether or not x is being specified as an offset from , should be 0 or 1.

## Examples:

lambertW(0.25)=0.203888

lambertW(0.5, 0, 0) = 0.351734

lambertW(0.75, 0, 1) = 0.286834

lambertW(-0.25, -1, 0) = -2.153292