When you use griddedInterpolant, then your x must have all of its columns the same, and the row values must be sorted. Your y must have all of its rows the same and the column values must be sorted.
[X,Y] = ndgrid(1:3, 4:7)
Here, X and Y are valid for griddedInterpolant(X,Y,V)
X(2,2) = 2.01; X(2,3) = 2.02; X(2,4) = 2.03
This X is not valid for griddedInterpolant because the columns are not all the same as each other.
There is a different major sorting order,
[X2, Y2] = meshgrid(1:3, 4:7)
For this arrangement, all of the rows of X2 are the same as each other and the columns are sorted.
These two orders are connected by
[Y3,X3] = meshgrid(4:7, 1:3);
X3, Y3
Anyhow, this "meshgrid" arrangement of data is not valid for griddedInterpolant.
Generally speaking, if you have meshgrid data, then you can
F = griddedInterpolant(x.',y.',u.',"spline","spline");
