In a method of analyzing a quantity having temporal and spatial variations a multidimensional output data array is formed. The multidimensional output data array comprises array positions arranged along at least a first data-axis and a second data-axis, such as a spatial axis and a temporal axis. Values of the quantity are entered in the multidimensional output data array. Values of the quantity at substantially the same instant are entered at respective positions in the multidimensional output data array at equal positions along the first data-axis. Values of the quantity at substantially the same spatial position are entered at respective positions in the multidimensional output data array at equal positions along the second data-axis.