# deltaUT1

Calculate difference between Coordinated Universal Time (UTC) and Principal Universal Time (UT1)

## Syntax

``DUT1=deltaUT1(utc)``
``[DUT1,DUT1Error]=deltaUT1(utc)``
``DUT1=deltaUT1(utc,Name,Value)``
``[DUT1,DUT1Error]=deltaUT1(utc,Name,Value)``

## Description

example

````DUT1=deltaUT1(utc)` calculates the difference between Coordinated Universal Time (UTC) and Principal Universal Time (UT1) for UTC, specified as a modified Julian date (MJD). By default, this function uses a prepopulated list of International Astronomical Union (IAU) 2000A Earth orientation (IERS) data. This list contains measured and calculated (predicted) data supplied by the IERS. The IERS measures and calculates this data for a set of predetermined dates. For dates after those listed in the prepopulated list, `deltaUT1` calculates the data by using this equation, limiting the values to +/- .9s:UT1-UTC=0.5309-0.00123(MJD-57808)-(UT2-UT1) `[DUT1,DUT1Error]=deltaUT1(utc)` returns the error for the difference between Coordinated Universal Time (UTC) and Principal Universal Time (UT1) for UTC.```

example

````DUT1=deltaUT1(utc,Name,Value)` calculates the difference between UTC and UT1 using additional options specified by one or more `Name,Value` pair arguments.`[DUT1,DUT1Error]=deltaUT1(utc,Name,Value)` returns the error for the difference between Coordinated Universal Time (UTC) and Principal Universal Time (UT1) for UTC.```

## Examples

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Calculate the difference between UT1 and UTC values for December 28, 2015.

```mjd = mjuliandate(2015,12,28) dUT1 = deltaUT1(mjd) ```
```mjd = 57384 dUT1 = 0.0886```

Calculate the difference between UT1 and UTC values for December 28, 2015 and January 10, 2016 using the custom file, aeroiersdata20170101.mat.

```mjd = mjuliandate([2015 12 28;2016 1 10]) dUT1 = deltaUT1(mjd,'Source','aeroiersdata20170101.mat')```
```mjd = 57384 57397 dUT1 = 0.0886 0.0648```

Calculate the difference between UT1-UTC values for December 28, 2015 and January 10, 2016 using the custom file, `aeroiersdata.mat`.

```mjd = mjuliandate([2015 12 28;2016 1 10]) [dUT1,dUT1Err] = deltaUT1(mjd,'Source','aeroiersdata.mat')```
```mjd = 57384 57397 dUT1 = 0.0886 0.0648 dUT1Err = 1.0e-05 * 0.3900 0.7300```

## Input Arguments

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Array of UTC dates, specified as an M-by-1 array, represented as modified Julian dates. Use the `mjuliandate` function to convert the UTC date to a modified Julian date.

### Name-Value Pair Arguments

Specify optional comma-separated pairs of `Name,Value` arguments. `Name` is the argument name and `Value` is the corresponding value. `Name` must appear inside quotes. You can specify several name and value pair arguments in any order as `Name1,Value1,...,NameN,ValueN`.

Example: 'Source','aeroiersdata.mat'

Custom list of Earth orientation data, specified in a MAT-file.

Out-of-range action, specified as a string.

Action to take in case of out-of-range or predicted value dates, specified as a string:

• Warning — Displays warning and indicates that the dates were out-of-range or predicted values.

• Error — Displays error and indicates that the dates were out-of-range or predicted values.

• None — Does not display warning or error.

Data Types: `string`

## Output Arguments

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Difference between UT1 and UTC, specified as an M-by-1 array.

Error for difference between UT1 and UTC (UT1-UTC), according to the International Astronomical Union (IAU) 2000A resolutions, specified as an M-by-1 array, in seconds.

## Compatibility Considerations

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Behavior changed in R2020b 