# Plotting two dependent function with respect to each other

I am writing a small code in Matlab to achieve following:

X, Y, and Z are all vectors and correspond to different physical quantities.

x1 and x2 are two different vectors made from allowed values which X can have.

Now I have Y as function of x1

Y=f(x1)

and Z as function of x2

Z=g(x2)

I do not know the functions 'f' and 'g' explicitly but I have a table which gives me Y and Z corresponding to x1 and x2 respectively.

So I can plot Y=f(x1) and Z = g(x2) in MATLAB using plotyy function using a common x-scale but 2 different y axis.

I want to plot Y as function of Z. What will be the most efficient way to do this? I guess I might need to use interpolation somewhere in this.

Thanks in advance !

## Answers

As mentioned by @mikkola, interpolation would be the way to go. You could interpolate Y onto the domain of Z, Z onto the domain of Y, or Y and Z onto a completely different domain. Do be careful though, as you want to make sure you interpolate, not extrapolate. The default for interp1 is linear interpolation, but you can get it to implement other types of interpolation by passing in an optional parameter.

The following is an example with two different domains x1 and x2, corresponding to functions Y=sin(x) and Z=cos(x). These are interpolated onto a different domain x3 so that Y and Z can be plotted against each other, yielding a circle as we would expect.

% Two different domains x1 = 0:0.02:2*pi; x2 = 0:0.03:2*pi; % Yielding two different functions Y = sin(x1); Z = cos(x2); % Interpolate them both onto a common domain (x3) x3 = 0:0.01:2*pi; Yi = interp1(x1,Y,x3); Zi = interp1(x2,Z,x3); % Plot - circle, as expected figure; plot(Yi,Zi)