Get the index of the Zernike coefficient for the given order and azimuthal frequency.
\[j = n(n+2) + m + (0 \text{ if } coord = 'x' \text{ else } 1)\]
- Parameters:
n (int) – The order of the Zernike polynomial.
m (int) – The azimuthal frequency of the Zernike polynomial.
coord (str) – The coordinate (‘x’ or ‘y’) for which to get the index.
- Returns:
The index of the Zernike coefficient in the parameters array.
- Return type:
int