This icon allows you to compute a set of percentiles of a given input fieldset. A percentile is a number such that the given percentage of a distribution is equal to or below it. For instance, the median is the 50th percentile - 50% of the values are equal to or below it.

The generated fields can simply be visualised or saved as GRIB files.

From Macro/Python this icon can be called as ** percentile()**.

## The Percentile Editor

### Data

Specifies the data required for the application. This can be any icon returning GRIB data (e.g. MARS Retrieval, GRIB Filter, Formula, Simple Formula). The icon field assist button provides a tailor made MARS request in case you need some guidance in the data specification. Alternatively, parameter **Source** can be used.

### Source

Specifies the GRIB file path and name. Alternatively, parameter **Data** can be used.

### Percentiles

Specifies a list of values from 0 to 100.

### Interpolation

Specifies the interpolation method used to compute the percentiles: **nearest_neighbour** or **linear.** The default value is: **nearest_neighbour**.

Given a list of numbers **V**, the algorithm used to compute a percentile is the following:

Compute the rank (R) of a P-th percentile. This is done using the following formula:

R = P/100 x (N + 1)

where**P**is the desired percentile and**N**is the number of input fields.Compute the percentile:

If R is an integer, the P-th percentile will be the number with rank R.

If R is not an integer, the P-th percentile is computed by interpolation as follows:

If the interpolation method is

**Nearest Neighbour**, the following equation is used:

P-th = V[int(R + 0.5)]If the interpolation method is

**Linear**, the following steps are used:Define IR as the integer portion of R

Define FR as the fractional portion or R

Find the scores with Rank IR and with Rank IR + 1, e.g. V[IR] and V[IR+1]

Interpolate by multiplying the difference between the scores by FR and add the result to the lower score, e.g.

Pth = FR * (V[IR+1] - V[IR]) + V[IR]