How to create exponential graph - plot

Question

How can I make an x-axis that doubles for every increment? I want equal distances between 0, 128, 256, 512, 1024 and 2048. How can I do that?
I'm trying to plot points from a benchmark where I measured time and doubled the memory size every increment.

Answer 1

You can cheat and plot with a linear axis, like from 1 up to as many numbers as you desire, then change the labels when you're done. You can use the 'xtick' property to set what horizontal tick values on your graph remain and the 'xticklabel' property to change the labels to your desired values.
labels = [0 128 256 512 1024 2048]; % Provide your labels here
x = 1 : numel(labels);
y = rand(1, numel(x)); % Insert your data here
plot(x, y, 'b.'); % Plot your data
set(gca, 'xtick', x); % Change the x-axis so only the right amount of ticks remain
set(gca, 'xticklabel', labels) % Change the labels to the desired ones
I get the following graph. Note that the data I'm plotting is completely random as I don't have your data but I want to demonstrate what the changed plot looks like:
For more properties that you can change on your graph, see the Axes Properties page on the Octave docs.

Answer 2

With apologies to Rayryeng, since I'm essentially proposing the same method at heart, but I felt it was missing important info, such as how to convert the axis itself to equally spaced intervals in the first place, without messing with the data. So here's a complete solution for example data X vs Y, producing the equivalent of semilogx for base 2.
Y = 1 : 10;
X = 2 .^ Y;
XTicks = log2(X);
XTickLabels = {};
for XTick = XTicks
XTickLabels{end+1} = sprintf('2^{%d}', XTick);
end
plot (log2 (X), Y);
set(gca, 'xtick', XTicks, 'xticklabel', XTickLabels);
Note that if you plan to 'superimpose' another plot on top of this, you'll have to take into account that the actual values in the X axis are essentially "1, 2, 3, ... 10", so either "log-ify" the new plot's X-axis values too, before superimposing via hold on, or plot onto another, independent set of axes entirely and place them in the same position.
Note: I have assumed that you're after a base-2 logarithmic x-axis. If you do actually want the 0-128 interval to be the same as the 128-256 interval, then modify as per Rayrengs answer --- or even better, use a more appropriate graph, like a bar graph! (i.e. with the 'powers-of-two' used purely as descriptive labels for each column)