Difficulties in axes scaling on matrices: 500 values should be 200 Hz - how to handle?

Hello community,

As described I have difficulties in scaling axes on 3d (or 2d) plots.

For example I have a 100x500 matrix = A

Due to the resolution in data aquisition I have 100 Values on the time axe y and 500 values on the frequency axe x.

I want an easy way in coding that those 500 values describing 200 Hz, and that those 100 Values describing 6 hours.

Until now I always changed the width of the matrix with a factor, so that I only have 200 values.

if true
  % maxfr1=zeros(109,1);
maxfr2=zeros(109,1);
maxfr3=zeros(109,1);
maxfr4=zeros(109,1);
for i1= 1:109
  maxfr1(i1,1)=maxidx_smooth1(i1,1)*0.39;
  maxfr2(i1,1)=maxidx_smooth2(i1,1)*0.39;
  maxfr3(i1,1)=maxidx_smooth3(i1,1)*0.39;
  maxfr4(i1,1)=maxidx_smooth4(i1,1)*0.39;
end  
end

When I plot a 2d or a 3d graph its shown correctly then. But this is very uncomfortable and erases my higher resolution in data aquisition. Until now I have not found a way to do it easily interactive (change ticks only adds or deletes values but is not changing the whole scale)...

I certainly need help :)

Thank you

Answer 1

[Jan]

At first you could cleanup the posted code - you do not nee a loop:

maxfr1 = maxidx_smooth1 * 0.39;
maxfr2 = maxidx_smooth2 * 0.39;
maxfr3 = maxidx_smooth3 * 0.39;
maxfr4 = maxidx_smooth4 * 0.39;

It would be even easier, if you store the vectors in one matrix.

But I assume, I do not understand the actual problem.

[EDITED]

It would be clearer, if you post Matlab code, which reproduces your problem. I assume you need to specify the values of the X-direction:

y = rand(50, 10);  % Smaller for simplicity
figure
plot(y);           % Your problem, x-values are the indices
figure
x = linspace(0, 200, 50);
plot(x, y);        % Scaled x-values

Answer 2

[Florian]

OK. I try to describe it easier.

I need a 2d plot of a matrix. The matrix has the dimensions 100x500.

I recorded the data in the matrix with 3 values per second for a higher resolution.

If I want to plot the matrix now - the x-axis goes from 0 to 500. Those 500 values representate lets say 200 Hz. So in the plot there shouldn´t be shown the number of values i have - "500" BUT INSTEAD the 200 Hz but on the same location where now "500" is...

If I do change "X-Limits" which is now from 0 to 500 into 0 to 200 it simply just cuts off the rest of the graph. But I want the whole graph displayed just with the x-axis scale 0 to 200.

I hope this was understandable - picture didn´t work.

Thanks

[Jan]

What does "picture didn't work" mean?

Instead of "if I want to plot..." post the corresponding code, because the actual problem is hidden in it.

[Florian]

Hello again,

sorry for confusion - in my head the problem description sounds logical ;)...

 if true
    % scale problems with plot
% %%create matrix
A = rand(109,512);
for i= 1:10
    A(:,40+i)=30;
end    
% %%create plot
figure1 = figure(1);
plot1 = surf(A);
%plot1 shows now a 3d plot with 512 values in x-direction, 109 in
%y-direction and 30 values in z-direction. the values of the x-direction
%are showing a frequency range from 20 to 200 Hz. This means i have to
%"rename" the x-axis scales that it is shown correctly in the figure.
%Otherwise someone who dont knows what i have done, thinks we have a
%frequency range from 0 to 500 Hz.  end

[Jan]

There is no reason for apologies, because you are the only one who suffers from missing answers.

Have you seen my new suggestion after the [EDITED] tag?

[Florian]

I have tried the linspace function and its pretty good. Sounds like that what I needed. Are there any ways to do this interactive - when the plot is already created?

Thanks

[Jan]

Yes.

Set(AxesHandle, 'XData', linspace(0, 200, 50))

The AxesHandle can ge found e.g. by clicking on the axes and using gca afterwards.

[Florian]

Ok works great now but just for 2d graphs....!!! Thank you very much for your effort !!!

Answer 3

[Florian]

ok as i told you the linspace function works with 2d plots.

but i have another problem with a 3d plot: Please try this

GG2 =rand(109,512);

figure43 = figure(43);
surf(GG2)

figure44 = figure(44);
x = linspace (20,200,2);
surf(x,GG2(:,1),GG2);

I do want the same graph than in figure43 but the x-axis range should go from 20 to 200 and not from 0 to 600.

The figure44 shows nothing...

Is this possible somehow?

Regards,