Semilogx plot does not plot part of my data

Hi,

I'm trying to plot calculated thicknesses of sedimentology flume experiments in a 2D plot with transported distance (x) and thickness (y).

The plot contains multiple lines (one for each grainsizeclass) and are added to the plot using the hold on command.

I want to make the x-axis logaritmic to better visualise the data.

% Plot total lobe geometery as a regular plot  
% advplot.sp is an array with sample points. 
% LobeThickness.grainsizeclass is the thickness of that grainsizeclass in the y-direction. 
F7 = figure('Name','Predicted Lobe Geometry');
plot(advplot.sp,LobeThickness.Total,'g'); 
hold on
plot(advplot.sp,advplot.Fsilt,'g');
hold on
plot(advplot.sp,advplot.Fvfsd1,'Color','[0.6 1 1]','linewidth',1.5);
hold off 
% my code plots up to 17 lines in one figure, I reduced it to 3 for this example 

% Plot total lobe geometery as semilogx plot 
F8 = figure('Name','Predicted Lobe Geometry');
plot(advplot.sp,LobeThickness.Total,'g');
hold on
plot(advplot.sp,advplot.Fsilt,'g');
hold on
plot(advplot.sp,advplot.Fvfsd1,'Color','[0.6 1 1]','linewidth',1.5);
hold off
set(gca,'FontSize',29','XScale', 'log') % this is the only difference with the plot above 

I know from the first plot that the maximum y value should be about 3.3. When making the semilogx plot it seems like part of the data is not plotted, the maximum y value in the plot is now ~ 0.15 m whilst it shouldn't change.

• I used the same method on other data, here the semilogx plot works fine (max y values are the same for plot (x,y) and semilogx(x,y).
• I tried adjusting the xlim and ylim values, this does not make a difference

I added a few figures which I think show what goes wrong.

Any help is much appreciated.

[Mathieu NOE]

hello

please remember that a loglog or semilogx plot cannot display the y value associated with x = 0

so if your maximum y value (about 3.3) correspond to x = 0 , it will not be displayed once you use loglog or semilogxg

[Pelle Adema]

Hi Mathieu NOE, thanks for the reply.

I checked what the x value for the higher y values should be. The value is at x = 0 but values between 2 and 3 should still show for values between x = 0 and x = 0.025.

I tried:

xlim([10e-3 1.2.*max(AdvLength.vf_sand1(:))]); % setting the  xlim   min to 10e-3  manually 

But this didn't solve the issue (see figure below).

[Mathieu NOE]

could you send me the data , please ?

[Pelle Adema]

As I was preparing the data to send them to you I finally saw what the issue was.

My sample points for the x axes are spaced by 0.05 and interpolated in between the points. As you pointed out the semilogx function cannot work with x is 0. I suppose it can therefore also not interpolate between log 0.05 and log 0, so these data are left out. I get the result that I need by changing the stepsize of my sample points array.

Thanks for helping out, definitely pointed me in the right direction.

[Mathieu NOE]

glad you find it !