set logscale <axes> {<base>} unset logscale <axes> show logscale
where 4#4axes5#5 may be any combinations of x, x2, y, y2, z, cb, and r in any order. 4#4base5#5 is the base of the log scaling (default is base 10). If no axes are specified, the command affects all axes except r. The command unset logscale turns off log scaling for all axes. Note that the ticmarks generated for logscaled axes are not uniformly spaced. See set xtics (p. ).
Examples:
To enable log scaling in both x and z axes:
set logscale xz
To enable scaling log base 2 of the y axis:
set logscale y 2
To enable z and color log axes for a pm3d plot:
set logscale zcb
To disable z axis log scaling:
unset logscale z