See if:
set(gca, 'XDir','reverse')
does what you want. That will reverse the x-axis direction, and the data associated with it, so the x-axis coordinates and the x-values of the data remain the same.
Otherwise, try something like this if you only want to reverse the axis labels and not the axis values themselves:
figure
plot(1:100, rand(1,100))
xt = get(gca, 'XTick');
xtr = linspace(max(xt), min(xt), numel(xt));
set(gca, 'XTick',xt, 'XTickLabel',sprintfc('%.1f', xtr))
you can also use the compose function:
set(gca, 'XTick',xt, 'XTickLabel',compose('%.1f', xtr))
