`ECH_ORDERNUM`

Determine the order number of a specified wavelength

Use the grating equation to calculate the free spectral range and then derive the order number directly from it.

`ECH_INIT`

must be called before calling this routine.

`CALL`

`ECH_ORDERNUM`

(W, `THETA`

, `GAMMA`

, M, `STATUS`

)

`READ` | W | `REAL` | Wavelength whose order number is to be determined (ie the order number within which it lies within the free spectral range) (Angstroms) |

`READ` | `THETA` | `REAL` | Echelle theta angle corresponding to the current configuration (radians) |

`READ` | `GAMMA` | `REAL` | Echelle gamma angle corresponding to the current configuration (radians) |

`WRITE` | M | `INTEGER` | Order number corresponding to wavelength |

`READ` , `WRITE` | `STATUS` | `INTEGER` | Global status value |

C.J. Hirst `UCL`

(`ZUVAD`

::`CJH`

)