(sw-econtract)=

# sw_econtract

## Syntax
  
`Qm = sw_econtract(Q,Name,Value)`
  
## Description
  
`Qm = sw_econtract(Q,Name,Value)` converts $(Q,E)$ values in the phase
space into $Q$ values as it would appear when measuring it with via
neutron diffraction.
  
## Input Arguments
  
`Q`
: Input values in reciprocal space in the scattering plane in
  Å$^{-1}$ units, dimensions are $[2\times n_Q]$.
  
## Name-Value Pair Arguments
  
`'E'`
: Energy transfer value in meV, default value is zero.
  
`'lambda'`
: Wavelength of the incident neutron beam in Å.
  
`'ki'`
: Momentum of the incidend neutron beam in Å$^{-1}$, alternative
  input to `lambda`.
  
`'sense'`
: Scattering sense:
 
  * `1`  detectors are on the right hand side from the incident beam direction, default.
  * `-1` detectors are on the left hand side from the incident beam direction.
  
## See Also
  
[sw_converter](#sw-converter)