How to add multiple axes to a log-log plot?

I would like to create a log-log-plot with multiple x-axes. My goal is to display my data 'y' as function of 'x' and as a function of 'u=a*x' simultaneously. I have seen examples of plots with multiple axes but did not come across any log-log plot. Is there a way to achieve this?

Any hint would be appreciated, Christian

Answer 1

[Thorsten]

You have to set the xscale and yscale property of ax2 to 'log':

x1 = 1:1000;
y1 = x1.^2;
x2 = 2*x1;
y2 = y1;
loglog(x1,y1,'r')
hold on,
ax2=axes('xaxislocation','top','yaxislocation','right','color','none', 'xscale', 'log', 'yscale', 'log')
hold on
loglog(x2,y2,'g')

[Christian]

Thanks! Now it works.

Answer 2

[Thorsten]

See http://www.mathworks.com/matlabcentral/answers/54258-plotting-two-loglog-y-axes

[Christian]

Thanks for pointing out this possibility. However, I'd like to have two different x-axis whereas a single y-axis is fine. 'plotyy' provides just the opposite.

Answer 3

[Azzi Abdelmalek]

Look at this example

x1=0:0.01:5
x2=10*x1
y1=sin(x1)
y2=2*cos(x2)
plot(x1,y1,'r')
hold on,
ax2=axes('xaxislocation','top','yaxislocation','right','color','none')
hold on
plot(x2,y2,'g')

[Christian]

Thanks for your suggestion which works fine for plots with a linear scale. As I want to create a log-log plot, I tried replacing the 'plot' commands by 'loglog' commands. Unfortunately, doing this, produces strange results.

For example:

x1 = 1:1000;
y1 = x1.^2;
x2 = 2*x1;
y2 = y1;
loglog(x1,y1,'r')
hold on,
ax2=axes('xaxislocation','top','yaxislocation','right','color','none')
hold on
loglog(x2,y2,'g')

This piece of code should produce two straight lines with the same slope. Instead, it creates a straight line and a parabola as the second set of axes has a linear scale.

Any idea how to overcome this problem?