How to get arrows on axes in MATLAB plot? - matlab

Question

I want to plot something like this:
x = 0:0.01:10;
f = #(x) 50* 1.6.^(-x-5);
g = #(x) 50* 1.6.^(+x-10);
plot(x, f(x));
hold on
plot(x, g(x));
I can't manage to get axes similar to the ones in this figure:
I know I can remove the top and right lines like in this question, but I don't know how to get the arrows on the edges.
I don't need the additional annotations, but I would like to remove the ticks on the axes. I know how to do this when the axes are "normal", but I'm not sure if it must be done in another way when the axes are already manipulated.
Does anyone know how to do this?

Answer 1

Well, don't say I didn't warn you :)
% Some bogus functions
f = #(x) 50* 1.6.^(-x-5);
g = #(x) 50* 1.6.^(+x-10);
% Point where they meet
xE = 2.5;
yE = f(xE);
% Plot the bogus functions
figure(1), clf, hold on
x = 0:0.2:5;
plot(x,f(x),'r', x,g(x),'b', 'linewidth', 2)
% get rid of standard axes decorations
set(gca, 'Xtick', [], 'Ytick', [], 'box', 'off')
% Fix the axes sizes
axis([0 5 0 5])
% the equilibrium point
plot(xE, yE, 'k.', 'markersize', 20)
% the dashed lines
line([xE 0; xE xE], [0 yE; yE yE], 'linestyle', '--', 'color', 'k')
% the arrows
xO = 0.2;
yO = 0.1;
patch(...
[5-xO -yO; 5-xO +yO; 5.0 0.0], ...
[yO 5-xO; -yO 5-xO; 0 5], 'k', 'clipping', 'off')
% the squishy wiggly line pointing to the "equilibrium" text
h = #(x)0.5*(x+0.2) + 0.1*sin((x+0.2)*14);
x = 2.7:0.01:3.5;
plot(x, h(x), 'k', 'linewidth', 2)
% the static texts
text(xE-yO, -0.2, 'Q^*', 'fontweight', 'bold')
text(-2*yO, yE, 'P^*', 'fontweight', 'bold')
text(-2*yO, 4, 'Price', 'rotation', 90, 'fontsize', 14)
text( 4, -0.2, 'Quantity', 'fontsize', 14)
text( .5, 4.2, 'Demand', 'fontsize', 14, 'rotation', -55)
text( 4.0, 3.3, 'Supply', 'fontsize', 14, 'rotation', +55)
text( 3.6, 2.1, 'Equilibrium', 'fontsize', 14)
Result:

Answer 2

The symbolic math toolbox has provisions for making these arrows, but without that toolbox you are stuck with drawing the arrows yourself. The following code should be useful for this purpose:
% determine position of the axes
axp = get(gca,'Position');
% determine startpoint and endpoint for the arrows
xs=axp(1);
xe=axp(1)+axp(3)+0.04;
ys=axp(2);
ye=axp(2)+axp(4)+0.05;
% make the arrows
annotation('arrow', [xs xe],[ys ys]);
annotation('arrow', [xs xs],[ys ye]);
% remove old box and axes
box off
set(gca,'YTick',[])
set(gca,'XTick',[])
set(gca,'YColor',get(gca,'Color'))
set(gca,'XColor',get(gca,'Color'))
The only drawback is that for some figure window sizes you will have a 1-pixel white border below the arrows, and setting the LineWidth property of the axes to a ridiculous small value does not help.
But for printing, the small white border should not be relevant.