How to get a Negative Positive Negative Y axis labels?

Hey Guys,

I have 3 column matrix which I would like to plot as a 3d surf plot with each column representing each axis. The values in Y axis increases from -0.4 to 1.4 and the decreases to -0.4 again. Something like

Y= [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];

The problem is when I plot it using surf function, the y axis looks like -0.4 to 1.4. and the data is plotted as such, but I would like to plot the values in y axis to first increase and decrease, similar to the data (so the Y axis must have labels same as the data - Negative Positive Negative). But I am always getting the y axis with just increasing values and the x and z values corresponding to the downward slope (1.4 to -0.4) is just plotted as an inverted surface. Is there a solution for this?

Thanks

Answer 1

[Star Strider]

The y-tick values must be increasing. However you can choose the y-tick labels to be (almost) whatever you want.

Try this:

Y= [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];
yt = get(gca, 'YTick');                                                         % Get Y-Tick Values
ytx = linspace(min(yt), max(yt), numel(Y));                                     % New Y-Tick Values
ytl = sprintfc('%.1f',Y);                                                       % New Y-Tick Labels
set(gca, 'YTick',ytx, 'YTickLabel',ytl)                                         % Set New Y-Tick Labels

I cannot test this because I do not have your data. It should work.

[Chockalingam Ramanathan]

Hey thanks a lot for your suggestion, however I guess I am doing some mistake. Can you tell me where am I going wrong? I have attached my code,data and the figure. Also can you suggest me another way to create a 3d colour map for a 3 column matrix?

x = data(:,1); %Time
y = data(:,2); %Voltage
z = data(:,3); %Current
figure(1);
xi=linspace(min(x),max(x),30);
yi=linspace(min(y),max(y),30);
[XI YI]=meshgrid(xi,yi);
ZI = griddata(x,y,z,XI,YI);
surf(XI,YI,ZI*1000);
yt = get(gca, 'yTick');                                                         
ytx = linspace(min(yt), max(yt), numel(y));                                     
ytl = sprintfc('%.1f',y);                                                       
set(gca, 'yTick',ytx, 'yTickLabel',ytl);   
colormap jet; 
cbh = colorbar;
shading interp; 
xlabel ('Time(in S)');
ylabel ('Voltage (in V)');
ylabel (cbh, 'Current(in nA)');

[Star Strider]

My pleasure.

I would change the ‘ytx’ and ‘ytl’ assignments to:

ytx = linspace(min(yt), max(yt), numel(y)/2000);                                     
ytl = sprintfc('%.1f',ytx); 

since this makes the y-tick values easier to read.

The entire code then becomes:

[data,S] = xlsread('data.xlsx');
x = data(:,1); %Time
y = data(:,2); %Voltage
z = data(:,3); %Current
figure(1);
xi=linspace(min(x),max(x),30);
yi=linspace(min(y),max(y),30);
[XI YI]=meshgrid(xi,yi);
ZI = griddata(x,y,z,XI,YI);
surf(XI,YI,ZI*1000);
view(-30, 30)
yt = get(gca, 'yTick');                                                         
ytx = linspace(min(yt), max(yt), numel(y)/2000);                                     
ytl = sprintfc('%.1f',ytx);                                                       
set(gca, 'yTick',ytx, 'yTickLabel',ytl, 'FontSize',6);   
colormap jet; 
cbh = colorbar;
shading interp; 
xlabel ('Time(in S)');
ylabel ('Voltage (in V)');
ylabel (cbh, 'Current(in nA)');

Note that I changed the number of ‘ytx’ values, and then use them to create ‘ytl’, so they all correspond. Change the divisor (here 2000) to change the number of ticks to be displayed.

To use your ‘Y’ vector:

Y = [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];

the ‘ytx’ and ‘ytl’ vectors change to become:

ytx = linspace(min(yt), max(yt), numel(Y));                                     
ytl = sprintfc('%.1f',Y); 

The rest of the code is unchanged:

Y = [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];
x = data(:,1); %Time
y = data(:,2); %Voltage
z = data(:,3); %Current
figure(1);
xi=linspace(min(x),max(x),30);
yi=linspace(min(y),max(y),30);
[XI YI]=meshgrid(xi,yi);
ZI = griddata(x,y,z,XI,YI);
surf(XI,YI,ZI*1000);
view(-30, 30)
yt = get(gca, 'yTick');                                                         
ytx = linspace(min(yt), max(yt), numel(Y));                                     
ytl = sprintfc('%.1f',Y);                                                       
set(gca, 'yTick',ytx, 'yTickLabel',ytl, 'FontSize',6);   
colormap jet; 
cbh = colorbar;
shading interp; 
xlabel ('Time(in S)');
ylabel ('Voltage (in V)');
ylabel (cbh, 'Current(in nA)');

[Chockalingam Ramanathan]

Hey thanks for your suggestion and time !

I guess i am going wrong somewhere...

this is the figure am getting for the first code, here the problem is that the y axis is plotted but I would want the y labels from negative to positive to negative as well as the data plotted as such. Which should be fine with your second code.

But here, the y labels are changed but the data is plotted the same way as before, so i guess the y label and the y data are not in sync.

to understand better i have attached a representative image below. The one on the left is what we have now, the one on the write is what I would like to have.

Could you please guide me with this problem? Thanks in advance.

[Star Strider]

My pleasure.

You initially indicated that you only wanted the axis labels to be different. Now, I am not certain what you want.

One option is to use the fftshift (or circshift) function:

ZI = fftshift(ZI,1);

that in context (I commented out the circshift call, so you can use it if you want a different number of index shifts) is:

Y = [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];
x = data(:,1); %Time
y = data(:,2); %Voltage
z = data(:,3); %Current
figure(1);
xi=linspace(min(x),max(x),30);
yi=linspace(min(y),max(y),30);
[XI, YI]=meshgrid(xi,yi);
ZI = griddata(x,y,z,XI,YI);
ZI = fftshift(ZI,1);
% ZI = circshift(ZI,fix(size(ZI,1)/2), 1);
surf(XI,YI,ZI*1000);
view(-115, 30)
yt = get(gca, 'YTick');                                                         
ytx = linspace(min(yt), max(yt), numel(Y)+1);                                     
ytl = sprintfc('%.1f',Y);                                                       
set(gca, 'YTick',ytx, 'YTickLabel',ytl, 'FontSize',6);   
colormap jet; 
cbh = colorbar;
shading interp; 
xlabel ('Time (in S)');
ylabel ('Voltage (in V)');
ylabel (cbh, 'Current(in nA)');

Change the dimension argument for fftshift (or circshift) if I am shifting the wrong one here.

[Chockalingam Ramanathan]

Ah..If you see my data the 2nd column (y) has values from negative to positive and negative again..which I would like to plot as such with the new Y label. If you see in the 2nd figure that i shared, only the Y label is changed but the data was plotted according to the old Y label..I just wanted to know how to do this...

[Star Strider]

I didn’t realise your data are actually gridded. You only need to reshape the vectors to create the matrices you need for the surf plot. That completely avoids the griddata call (that you don’t need with already gridded data unless you want to resample it at a different resolution), and simplifies everything else.

It is now simply:

[data,S] = xlsread('Cdata.xlsx');
x = data(:,1); %Time
y = data(:,2); %Voltage
z = data(:,3); %Current
[Uy,ia,ix] = unique(y);

Xr = reshape(x,numel(Uy),[]);
Yr = reshape(y,numel(Uy),[]);
Zr = reshape(z,numel(Uy),[]);

figure
surf(Xr, Yr, Zr)
grid on
Y = [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];
yt = get(gca, 'YTick');                                                         
ytx = linspace(min(yt), max(yt), numel(Y)+1);                                     
ytl = sprintfc('%.1f',Y);                                                       
set(gca, 'YTick',ytx, 'YTickLabel',ytl, 'FontSize',6);  
colormap jet; 
cbh = colorbar;
shading interp; 
xlabel ('Time (in S)');
ylabel ('Voltage (in V)');
ylabel (cbh, 'Current(in nA)');

and the plot is:

This follows your designation of the variables and axes.

[Star Strider]

Chockalingam Ramanathan’s Answer moved here:

ahh..okay thanks for clearing things up...but if you see the cursor on the figure, Y value is 1.3 but the corresponding axis label is around -0.4 (this is what i meant by data not getting plotted in sync with the axis)..!

[Star Strider]

The tick labels you want do not re-define the original tick values.

There is not a 1:1 correspondence:

Y = [-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4];
ytx = linspace(min(Yr(:,1)), max(Yr(:,1)), numel(Y)); 
figure
plot(Y, ytx)
grid
xlabel('Defined Y-Tick Value')
ylabel('Actual Y-Tick Value')

Since my Answer does not appear to be what you want, I will delete it later.

[Chockalingam Ramanathan]

is it possible to use my original values as my Y tick values then?

[Star Strider]

If by ‘original values’ you mean ‘Yr(:,1)’ (that are repeated in every column of ‘Yr’), that is the only way. The values in your ’Y’ vector are only to show on the plot. They do not reflect the actual values in the matrices or the axes.

[Chockalingam Ramanathan]

Okay..thanks a lot for your help..!

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!