MATLAB Answers

Abed Alnaif

Labeling Minor Tick Marks in Plots

Asked by Abed Alnaif
on 6 Oct 2011

Hi, I am trying (without success) to find a way to automatically label the minor tick marks in a plot -- specifically, a semi-log-y plot. I thought that I would be able to do this using the get(gca,...) command to obtain the locations of the minor tick marks, and then the set(gca,'YTick',...) command to set the minor ticks as major ticks. However, I wasn't able to figure out how to obtain the locations of the minor ticks using the get(gca,...) command. Please let me know if you have a solution. An example code is shown below:

function label_minor_ticks()
    figure
    y = [0.4,0.5,0.8,1,1.5,2,4];
    semilogy(y);
end

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2 Answers

Answer by Grzegorz Knor
on 6 Oct 2011
 Accepted answer

Remove YMinorTicks, and add new YTicks:

y = [0.4,0.5,0.8,1,1.5,2,4];
semilogy(y);
set(gca,'yMinorTick','off')
yRange = get(gca,'ylim');
p = ceil(log(yRange) / log(10));%nextpow10
ticks = [];
for k=p(1):p(2)
    if k==p(1)
        ticks = [ticks yRange(1):10^(k-1):10^k];
    elseif k==p(2)
        ticks = [ticks 10^(k-1)+10^(k-1):10^(k-1):yRange(2)];
    else
        ticks = [ticks 10^(k-1)+10^(k-1):10^(k-1):10^(k-1)];
    end
end
set(gca,'ytick',ticks(2:end-1))

This loop does not look good for me, but it works :)

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Answer by Abed Alnaif
on 6 Oct 2011

Thanks! I thought that there would be an easier way. I noticed one minor error in your solution, and I made a few other minor changes:

figure
y = [0.32,0.4,0.5,0.8,1,1.5,2,4,4.5,9.9,10.5];
semilogy(y);
set(gca,'yMinorTick','off')
min_y = min(y);
max_y = max(y);
most_sig_position_min = 10^floor((log10(min_y)));
most_sig_digit_min = floor(min_y / most_sig_position_min);
min_yaxis = most_sig_digit_min * most_sig_position_min;
most_sig_position_max = 10^floor((log10(max_y)));
most_sig_digit_max = ceil(max_y / most_sig_position_max);
max_yaxis = most_sig_digit_max * most_sig_position_max;
p(1) = ceil(log10(min_yaxis));
p(2) = ceil(log10(max_yaxis));
ticks = [];
for k=p(1):p(2)
    if k==p(1)
        ticks = [ticks min_yaxis:10^(k-1):10^k];
    elseif k==p(2)
        ticks = [ticks 10^(k-1)+10^(k-1):10^(k-1):max_yaxis];
    else
        ticks = [ticks 10^(k-1)+10^(k-1):10^(k-1):10^k];
    end
end
set(gca,'ytick',ticks())
axis([-Inf Inf min_yaxis max_yaxis])

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