I'm not 100% certain I understand, but here are steps toward what I think you want. Use some or all of them.
First version, I am only renaming your variables to what the actually represent, for my own sanity.
z= [0 2.3 4.9 9.1 13.7 18.3 22.9 27.2]; %z data
T=[22.8 22.8 22.8 20.6 13.9 11.7 11.1 11.1];%temperature data
coefs=polyfit(z,T,7); %interpolating polynomial coefficients
pint=polyval(coefs,z); %interpolating polynomial
plot(z, T, 'o', z, pint, '-');
xlabel('z');
ylabel('T');
legend('polynomial interpolation')
Next, I am swapping the axes for plotting, because it seems like maybe that is what you want?
z= [0 2.3 4.9 9.1 13.7 18.3 22.9 27.2]; %z data
T=[22.8 22.8 22.8 20.6 13.9 11.7 11.1 11.1];%temperature data
coefs=polyfit(z,T,7); %interpolating polynomial coefficients
pint=polyval(coefs,z); %interpolating polynomial
plot(T,z, 'o', pint,z, '-');
xlabel('T');
ylabel('z');
legend('polynomial interpolation')
Finally, I am changing the direction of the "Y" axis (which is plotting the variable z):
z= [0 2.3 4.9 9.1 13.7 18.3 22.9 27.2]; %z data
T=[22.8 22.8 22.8 20.6 13.9 11.7 11.1 11.1];%temperature data
coefs=polyfit(z,T,7); %interpolating polynomial coefficients
pint=polyval(coefs,z); %interpolating polynomial
plot(T,z, 'o', pint,z, '-');
set(gca,"YDir","reverse") % <--------- Here is where I reverse the direction of the axis
xlabel('T');
ylabel('z');
legend('polynomial interpolation')
I'm honestly not sure which of these things you really need, but maybe you can figure it out from these ideas.
