explain ax=gca; in matlab

gca stands for "get current axes". The ax variable is assigned the handle to the current axes object in the figure. This allows us to modify properties of the current axes, such as changing the x or y limits, setting the axis labels, adding gridlines, etc. For example, we may want to change the color of the axis labels as follows:

main.m
ax = gca;
ax.XColor = 'red';
ax.YColor = 'green';
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This will set the x-axis labels to be red and y-axis labels to be green.