# FilterFunction

`class boulderopal.graph.FilterFunction(operation, frequencies, exact)`

A tensor-valued filter function result.

### Variables

**inverse_powers**(*Tensor*) – The values of the filter function at the given frequencies.**uncertainties**(*Tensor**,**optional*) – The uncertainties of the filter function values. This field is None when the exact method is used for computing the filter function.**frequencies**(*np.ndarray*) – The frequencies at which the filter function has been evaluated.**value_shape**(*tuple**[**int**]*) – The shape of the function value.**exact**(*bool*) – Indicates whether filter function is exact.**name**(*str*) – The name assigned to the node.

### SEE ALSO

`Graph.filter_function`

: Evaluate the filter function for a control Hamiltonian and a noise operator at the given frequency elements.

## Notes

The value of a FilterFunction node can be fetched in a graph calculation by adding its name in the output_node_names parameter for the function call. This will add an item to the output dictionary in the calculation result object, whose key is name. The item’s value will be a dictionary with NumPy arrays with the “frequencies” and “inverse_powers” values. If the filter function calculation is not exact, the dictionary also contains an array with the filter function “uncertainties”.