# How to place the x axis pointing downward and the y axis horizontally?

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Matilde Santos on 26 Mar 2024
Answered: the cyclist on 26 Mar 2024
I have one project in which one of the questions asks to interpolate the temperature of a lake as a function of its depth. The tricky part is, the teacher wants the x axis pointing downwards ( which means the depth is increasing as we go down) and the y axis horizontally. So far I have researched about this and found no anwers. Does anyone know how to?
x= [0 2.3 4.9 9.1 13.7 18.3 22.9 27.2]; %z data
y=[22.8 22.8 22.8 20.6 13.9 11.7 11.1 11.1];%temperature data
coefs=polyfit(x,y,7); %interpolating polynomial coefficients
pint=polyval(coefs,x); %interpolating polynomial
plot(x, y, 'o', x, pint, '-');
xlabel('z');
ylabel('T');
legend('polynomial interpolation')

the cyclist on 26 Mar 2024
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.