openpiv.gpu.validation.Validation._mean_validation uses median_tol instead of mean_tol #33

Summary

In openpiv/gpu/validation.py, scalar mean validation appears to use the wrong tolerance parameter. The _mean_validation() method computes the local mean residual, but passes self.median_tol to _neighbour_validation() instead of self.mean_tol.

Current behaviour

Current code in Validation._mean_validation():

def _mean_validation(self):
    for k in range(self._num_fields):
        f_mean_residual = _gpu_residual(
            self._mean[k],
            self._neighbours[k],
            self._neighbours_present,
            "mean_residual",
        )
        self.val_locations = _neighbour_validation(
            self._f[k],
            self._mean[k],
            f_mean_residual,
            self.median_tol,
            self.val_locations,
        )

Expected Behaviour

Scalar mean validation should use self.mean_tol:

self.val_locations = _neighbour_validation(
    self._f[k],
    self._mean[k],
    f_mean_residual,
    self.mean_tol,
    self.val_locations,
)

Why this looks like a bug

• Validation.__init__ exposes separate median_tol and mean_tol parameters.
• _median_validation() correctly uses self.median_tol.
• _mean_validation_vec2d() correctly uses self.mean_tol.
• _rms_validation() correctly uses self.rms_tol.
• The scalar _mean_validation() path is the only path using another validation method's tolerance.

Impact

Users who configure mean_tol separately from median_tol get unexpected validation masks.

For example:

validation_method = "mean_velocity"
median_tol = 2
mean_tol = 5

The scalar validation still uses 2, not 5, making mean validation stricter than requested.

Suggested fix

Change this line in _mean_validation():

self.median_tol

to:

self.mean_tol

Suggested test

Add a test where median_tol and mean_tol differ, then assert scalar mean validation matches a direct _neighbour_validation(..., tol=mean_tol) reference.

Current tests use default equal values (MEDIAN_TOL == MEAN_TOL == 2) in the direct mean-validation test, so the bug is masked.