(spinw-setmatrix)=

# spinw.setmatrix method

## Syntax
  
`setmatrix(obj,Name,Value)`
  
## Description
  
`setmatrix(obj,Name,Value)` sets the value of a selected matrix based on
symmetry analysis.
  
## Examples
  
This example will set 'J1' coupling to the 6th symmetry allowed matrix,
with prefactor 0.235.
```matlab
setmatrix(crystal,'label','J1','pref',{[6 0.235]})
```
This will set 'J2' to antiferromagnetic Heisenberg exchange, with value
of 1.25 meV.
```matlab
setmatrix(crystal,'label','J2','pref',{1.25})
```
 
## Input Arguments
  
`obj`
: [spinw](#spinw) object.
  
## Name-Value Pair Arguments
  
One of the below options has to be given:
  
`'mat'`
: Label or index of the matrix that is already assigned to
  a bond, anisotropy or g-tensor.
  
`'bond'`
: Index of the bond in `spinw.coupling.idx`, e.g. 1 for first neighbor.
  
`'subIdx'`
: Selects a certain bond within the symmetry equivalent bonds, within
  default value is 1.
  
`'aniso'`
: Label or index of the magnetic atom that has a single ion
  anisotropy matrix is assigned, e.g. `'Cr3'` to select anisotropy on
  atoms with this label.
  
`'gtensor'`
: Label or index of the magnetic atom that has a g-tensor is 
  assigned.
  
Optional inputs:
  
`'pref'`
: Defines prefactors as a vector for the symmetry allowed
          components in a row vector with $n_{symMat}$ number of elements. Alternatively, if only
          a few of the symmetry allowed matrices have non-zero
          prefactors, use:
  ```matlab
  {[6 0.1 5 0.25]}
  ```
  This means, the 6th symmetry allowed matrix have prefactor 0.1,
          the 5th symmetry allowed matrix have prefactor 0.25. Since
          Heisenberg isotropic couplings are always allowed, a cell with
          a single element will create a Heisenberg coupling, example:
  ```matlab
  {0.1}
  ```
  This is identical to `obj.matrix.mat = eye(3)*0.1`.
          For DM interactions (antisymmetric coupling matrices), use
          three element vector in the cell:
  ```matlab
  {[D1 D2 D3]}
  ```
  In this case, these will be the prefactors of the 3
          antisymmetric symmetry allowed matrices. In case no crystal
          symmetry is defined, these will define directly the components
          of the  DM interaction in the $xyz$ coordinate system. Be
          carefull with the sign of the DM interaction, it depends on the
          order of the two interacting atoms! Default value is `{1}`.
          For anisotropy matrices antisymmetric matrices are not allowed.
  
## Output Arguments
  
The selected `obj.matrix.mat` will contain the new value.
  
## See Also
  
[spinw](#spinw) \| [spinw.gencoupling](#spinw-gencoupling) \| [spinw.getmatrix](#spinw-getmatrix)
  
*[DM]: Dzyaloshinskii-Moriya