Sometimes datasets are provided in matrix form, with first
index corresponding to longitudes ranging from 0 to 360.
matrixShiftLongitude cuts such matrices at
longitude=180, and swaps the pieces so that the dateline
is at the left of the matrix, not in the middle.
matrixShiftLongitude(m, longitude)The matrix to be modified.
A vector containing the longitude in the 0-360 convention. If missing,
this is constructed to range from 0 to 360, with as many elements as the first index of m.
A list containing m and longitude, both rearranged as appropriate.