MATLAB: Adding tick marks without overriding existing marks

semilogtickmarksxtick

I would like to add a tick mark to a semilogx() plot to indicate the -3dB point of my transfer function. I know that I can use (gca,'XTick',[ … ]) to add tick marks at specific frequencies; however, this forces the plot to ONLY display my specified tickmarks and completely removes the existing grid. is there anyway to add a tick mark overlay that maintains the standard semilog grid?
Note: the professor for this class had figures in his notes that do what I would like to do, but he has a pretty strict no-contact policy during take-home-exam weekends.

Best Answer

Play around with this:
>> x = 5.7;
>> yV = get(gca,'ylim');
>> text(x,yV(1),num2str(x),'VerticalAlignment','top','HorizontalAlignment','center')
>> line([x,x],yV)
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