heyoka.model.pm_xp

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heyoka.model.pm_xp#

heyoka.model.pm_xp(time_expr: expression = heyoka.time, eop_data: eop_data = eop_data()) → expression#

Derivative of the polar motion (x component).

Added in version 7.3.0.

This function will return an expression representing the first-order derivative of the \(x\) coordinate of the polar motion as a function of the input time expression time_expr. time_expr is expected to represent the number of Julian centuries elapsed since the epoch of J2000 in the terrestrial time scale (TT). eop_data is the Earth orientation parameters dataset to be used for the computation.

This quantity is modelled as a piecewise constant function of time, where the switch points are given by the dates in eop_data. Evaluation outside the dates range of eop_data will produce a value of NaN.

The return value is expressed in radians per Julian century (TT).

Parameters:

  • time_expr – the input time expression.

  • eop_data – the EOP data to be used for the computation.

Returns:

an expression for the derivative of the x component of the polar motion as a function of time.

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