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Grid [clist]Control the plotting of a grid, where [clist] is one or more of ON, OFf, X # #, Y # #. For Grid ON, the major tic marks are expanded to place a grid over the entire plot. Grid OFf turns off the grid replacing the tic marks. PGPLOT automatically selects the location of the major and minor tic marks. The Grid command allows you to override this selection. For example, Grid X 10,2 would divide the x-axis into 10 major divisions and then divide each major division into 2 minor divisions. Use Grid X 0,0 to go back to the default grid. The number -1 can be used to suppress the plotting of tic marks. Thus, Grid X -1 0 would only plot minor tic marks on the x-axis and Grid Y -1 -1 would prevent any tic marks from being plotted on the y-axis.
IMPORTANT: PGPLOT only places major tic marks at locations where the least significant digit of the range increments by integer amounts. If you attempt to force PGPLOT to violate this condition, then unexpected things may happen. For example, suppose you had used R Y 0 .15, in which case the range is 0.15 and the least significant digit is 0.01. Then using Grid Y 3,2 would place grid lines at intervals of 0.05. However, if you had tried Grid Y 2,2, then the grid lines would occur at intervals of 0.075, where the last digit (5) is not a significant digit. In this case, the plot will be incorrectly labeled. Grid X 1.5,2 is legal and would correctly produce labels at intervals of 0.1. (Of course, only one label would actually be plotted in this case.)
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