# eeqq2nqi.m

Converts the C_q and eta_q quadrupolar interaction specification convention into a 3x3 interaction matrix in Hz.

## Syntax

    Q=eeqq2nqi(C_q,eta_q,I,euler_angles)


## Arguments

    C_q          - quadrupolar coupling constant e^2*q*Q/h
in Hz

eta_q        - quadrupolar tensor asymmetry parameter

I            - spin quantum number

euler_angles - vector of three Euler angles in radians,
giving the orientation of the principal
axis frame relative to the lab frame.


## Outputs

    Q            - quadrupolar coupling tensor as a 3x3
matrix in Hz


## Examples

Most quadrupolar NMR examples in examples/nmr_solids and examples/optimal_control make use of this function.

## Notes

We do not recommend storing quadrupolar tensors in Cq/eta_q format - the 3x3 matrix is always better. This function is provided for historical compatibility reasons.