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Colormap - contourf scaling and color distribution

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Mepe
Mepe on 30 May 2020
Commented: Adam Danz on 30 May 2020
Hi,
I want to plot the matrix M_2f1 with the contourf command (logarithmic scaling). So far this works quite well.
But two points bother me:
1. I would like to specify a defined area in the colorbar (e.g. 0 to 10). Here, logarithmic scaling is certainly a hindrance. Is there another option than choosing a very small, positive value?
2. I don't like the color distribution in the colorbar. I would prefer an even distribution (detached from the logarithmic scaling)
M_2f1=[0.0149766610154867,0.0148727404855169,0.0149659744686933,0.0197882778625291,0.0184313013563117,0.0176794194615834,0.0196108762871584,0.0258284889924015,0.0354233801633032,0.171924195188659,0.0281396699959042,0.0141469884838954,0.0334375924402216,0.0314806724042401,0.172885272977384,0.0883818321056840,0.106217236988698,0.0782668761035103,0.122073669629712,0.0274013525228684,0.0485163365474854;0.0250969531529632,0.0139275587788499,0.0130272875683284,0.0198185099934251,0.0258483008607248,0.0216474128550250,0.0260883732887959,0.0329091753710079,0.0268783125653000,1.91538463836732,0.195449696327352,0.0381036869089853,0.0588836876081499,0.171757614634871,0.0231260787399225,0.170935395044788,0.120483617869003,0.600468182457506,0.166605755383242,0.318424884533997,0.0370178336952820;0.0127170974716373,0.0147177357124663,0.0142949618281963,0.0141321097009308,0.0135950246696883,0.0155180804843015,0.0128687984781713,0.0162524560391073,0.0149971936741940,0.0137489964554028,0.0328922058840716,0.0135826966044079,0.0147869975187494,0.0136696060929059,0.0133113468539191,0.0684702636256040,0.0644115870564511,0.359497603819481,0.0386968843910783,0.0148698983598170,0.0194361839183835]
f = figure(1);
axes1 = axes('Parent',f);
hold(axes1,'on');
[C,h]=contourf(log(M_2f1),15);
h.LineWidth = 0.0001;
box(axes1,'on');
axis(axes1,'tight');
set(axes1,'BoxStyle','full','Layer','top');
set(gca,'colorscale','log')
colorbar(axes1);
c = colorbar;
colormap(parula(15));
c.Label.String = 'Nonlinearity parameter';
set(c, 'ylim', [0 10])
xticks([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21])
xlim([1 21])
xticklabels({'','',5,'',10,'',15,'',20,'',25,'',30,'',35,'',40,'',45,'',50})
yticks([1 2 3])
ylim([1 3])
yticklabels({'0','5','10'})
xlabel('X-direction [mm]')
ylabel('Y-direction [mm]')
Any Idea?

Accepted Answer

Adam Danz
Adam Danz on 30 May 2020
Edited: Adam Danz on 30 May 2020
Here are the changes I suggest you make. Lines that have been commented-out are lines you don't seem to need.
The key changes are setting the x and y values in contourf() instead of setting tick labels and removing the log scale for the colorscale.
I've left additional comments in all caps with further explanation.
M_2f1=[0.0149766610154867,0.0148727404855169,0.0149659744686933,0.0197882778625291,0.0184313013563117,0.0176794194615834,0.0196108762871584,0.0258284889924015,0.0354233801633032,0.171924195188659,0.0281396699959042,0.0141469884838954,0.0334375924402216,0.0314806724042401,0.172885272977384,0.0883818321056840,0.106217236988698,0.0782668761035103,0.122073669629712,0.0274013525228684,0.0485163365474854;0.0250969531529632,0.0139275587788499,0.0130272875683284,0.0198185099934251,0.0258483008607248,0.0216474128550250,0.0260883732887959,0.0329091753710079,0.0268783125653000,1.91538463836732,0.195449696327352,0.0381036869089853,0.0588836876081499,0.171757614634871,0.0231260787399225,0.170935395044788,0.120483617869003,0.600468182457506,0.166605755383242,0.318424884533997,0.0370178336952820;0.0127170974716373,0.0147177357124663,0.0142949618281963,0.0141321097009308,0.0135950246696883,0.0155180804843015,0.0128687984781713,0.0162524560391073,0.0149971936741940,0.0137489964554028,0.0328922058840716,0.0135826966044079,0.0147869975187494,0.0136696060929059,0.0133113468539191,0.0684702636256040,0.0644115870564511,0.359497603819481,0.0386968843910783,0.0148698983598170,0.0194361839183835]
f = figure(1);
axes1 = axes('Parent',f);
hold(axes1,'on');
% [C,h]=contourf(log(M_2f1),15)
[C,h]=contourf(0:2.5:50, 1:3, log(M_2f1),15); % SET THE X AND Y VALUES HERE
h.LineWidth = 0.0001;
box(axes1,'on');
% axis(axes1,'tight'); % THE PLOT SHOULD ALREADY BE 'TIGHT', BUT YOU COULD KEEP THIS IF YOU WANT TO
set(axes1,'BoxStyle','full','Layer','top');
% set(gca,'colorscale','log') % IT'S NOT CLEAR WHY YOU NEED THIS
c = colorbar(axes1); % GET THE COLORBAR HANDLE HERE
% c = colorbar; % REDUNDANT
% colormap(parula(15));
c.Label.String = 'Nonlinearity parameter';
% set(c, 'ylim', [0 10]) % NO NEED FOR THIS
% xticks([1:21]) % NO NEED FOR THIS
% xlim([1 21]) % NO NEED FOR THIS
% xticklabels({'','',5,'',10,'',15,'',20,'',25,'',30,'',35,'',40,'',45,'',50}) % NO NEED FOR THIS
% yticks([1 2 3]) % YOU COULD KEEP THIS ONE IF YOU WANT TO
% ylim([1 3]) % NO NEED FOR THIS
% yticklabels({'0','5','10'}) % NO NEED FOR THIS
xlabel('X-direction [mm]')
ylabel('Y-direction [mm]')
One reason the image seems stretched vertically is because of the scaling difference between the x and y axes. That could be addressed by equating the aspect ratio using axis(axes1, 'equal') but then your axis height will be narrow.
  2 Comments
Adam Danz
Adam Danz on 30 May 2020
Do you mean something like this?
c.TickLabels = compose('10^{%.2g}',c.YTick);

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