# Pure to mixed

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pure_to_mixed | |

Converts a state vector or density matrix representation of a state to a density matrix | |

Other toolboxes required | none |
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Function category | Helper functions |

This is a helper function that only exists to aid other functions in QETLAB. If you are an end-user of QETLAB, you likely will never have a reason to use this function. |

` pure_to_mixed` is a function that convert's a state's current representation (either as a pure state vector or as a density matrix) into a density matrix. This function just exists to make the code within some other functions a bit cleaner.

## Syntax

`RHO = pure_to_mixed(PHI)`

## Argument descriptions

`PHI`: A density matrix or a pure state vector.

## Examples

The following code shows that if `v` is a pure state vector then `pure_to_mixed(v) == v*v'`, yet if `rho` is a density matrix then `pure_to_mixed(rho) == rho`.

```
>> v = RandomStateVector(2)
v =
0.6732 - 0.5736i
0.3190 + 0.3407i
>> pure_to_mixed(v)
ans =
0.7822 0.0193 - 0.4123i
0.0193 + 0.4123i 0.2178
>> pure_to_mixed(v*v')
ans =
0.7822 0.0193 - 0.4123i
0.0193 + 0.4123i 0.2178
>> v*v'
ans =
0.7822 0.0193 - 0.4123i
0.0193 + 0.4123i 0.2178
```

## Source code

Click here to view this function's source code on github.