Unwanted contour lines generated by contour()

Question

Dominic Babula 2023-10-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2034494-unwanted-contour-lines-generated-by-contour

编辑： Chunru 2023-10-17

Hi,

I can't seem to figure out why contour() is plotting the additional contours on the outer edge of the shape produced by pcolor().

The following function was used to calculate the values for the matrix M used to create the pcolor plot;

function val = TBM(theta,beta,M_upstream,g)
    % Description: TBM function solves Theta-Beta-Mach Relation for required values
    
    % Specifying option to turn off fsolve dialogue in the command window
    option = optimset('Display','off');
    % Solving for theta
    % Identifying required variable
    if theta == 0
        % Creating function handle of TBM equation in terms of required
        % variable
        TBM_eq = @(theta) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);
        
        % Solving equation for required variable
        val = fsolve(TBM_eq,0.1,option);
    
    % Solving for beta
    elseif beta == 0
        TBM_eq = @(beta) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);
        val = fsolve(TBM_eq,0.1,option);
    % Solving for upstream Mach number
    elseif M_upstream == 0
        TBM_eq = @(M_upstream) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);
        val = fsolve(TBM_eq,0.1,option);
    end
end

The following code produces the plot;

clear all; close all; clc

% Values

g = 1.4; % Ratio of specific heats for given gas

% Define the range of theta and beta values

theta = 0.5:0.5:50; % Range of theta from 0 to 50 degrees

beta = linspace(90,0.5,length(theta)); % Range of beta from 0 to 90 degrees

% Calculate Mach numbers for every theta beta combination

Mach = zeros(length(theta),length(beta));

for i = 1:1:length(theta)

for j = 1:1:length(beta)

M = TBM(theta(i),beta(j),0,g); % Mach number calculated using a function

if M <= 10

Mach(j,i) = M;

end

%%

% Create the heatmap for specified Mach numbers

figure("Name","Theta-Beta-Mach Relation Plot");

h = pcolor(theta,beta,Mach); % Pseudocolor plot used instead of heatmap

colormap turbo

c = colorbar;

c.Label.String = "M";

h.EdgeColor = "None";

hold on

% Add contours to heatmap

M_cont = [1.1:0.1:2 2.1:0.2:4 4.25:0.25:5 6 7 8 10];

[c,h] = contour(theta,beta,Mach,M_cont,"EdgeColor","w");

clabel(c,h,"FontSize",8,"Color","w")

xlabel("Theta (degrees)");

ylabel("Beta (degrees)");

title("Theta-Beta-Mach Relation");

As shown above, the additional contours produce the thick white outline.

Any help is greatly appreciated. Thanks!

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Answer 1

Chunru 2023-10-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2034494-unwanted-contour-lines-generated-by-contour#answer_1334514

编辑：Chunru 2023-10-17

在 MATLAB Online 中打开

Yo5ur function curve has very abrupt change near the ege (see one vertical slice of data). Therefore you will see many contour lines near the edge (to the dark color). Check out if the generated data is what you expect.

clear all; close all; clc

% Values

g = 1.4; % Ratio of specific heats for given gas

% Define the range of theta and beta values

theta = 0.5:0.5:50; % Range of theta from 0 to 50 degrees

beta = linspace(90,0.5,length(theta)); % Range of beta from 0 to 90 degrees

% Calculate Mach numbers for every theta beta combination

% Mach = zeros(length(theta),length(beta));

Mach = nan(length(theta),length(beta));

for i = 1:1:length(theta)

for j = 1:1:length(beta)

M = TBM(theta(i),beta(j),0,g); % Mach number calculated using a function

if M <= 10

Mach(j,i) = M;

end

%%

% Create the heatmap for specified Mach numbers

figure("Name","Theta-Beta-Mach Relation Plot");

h = pcolor(theta,beta,Mach); % Pseudocolor plot used instead of heatmap

colormap turbo

c = colorbar;

c.Label.String = "M";

h.EdgeColor = "None";

hold on

% Add contours to heatmap

M_cont = [1.1:0.1:2 2.1:0.2:4 4.25:0.25:5 6 7 8 10];

%M_cont = [1.1:0.1:2 2.1:0.3:2.7 ];

% M_cont = [2.7 2.7]

[c,h] = contour(theta,beta,Mach,M_cont,"EdgeColor","w");

clabel(c,h,"FontSize",8,"Color","w")

xlabel("Theta (degrees)");

ylabel("Beta (degrees)");

title("Theta-Beta-Mach Relation");

whos

Name Size Bytes Class Attributes M 1x1 8 double M_cont 1x28 224 double Mach 100x100 80000 double beta 1x100 800 double c 2x4823 77168 double g 1x1 8 double h 1x1 8 matlab.graphics.chart.primitive.Contour i 1x1 8 double j 1x1 8 double theta 1x100 800 double

figure

plot(Mach(:, 50)) % a verticle slice of data

function val = TBM(theta,beta,M_upstream,g)

% Description: TBM function solves Theta-Beta-Mach Relation for required values

% Specifying option to turn off fsolve dialogue in the command window

option = optimset('Display','off');

% Solving for theta

% Identifying required variable

if theta == 0

% Creating function handle of TBM equation in terms of required

% variable

TBM_eq = @(theta) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);

% Solving equation for required variable

val = fsolve(TBM_eq,0.1,option);

% Solving for beta

elseif beta == 0

TBM_eq = @(beta) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);

val = fsolve(TBM_eq,0.1,option);

% Solving for upstream Mach number

elseif M_upstream == 0

TBM_eq = @(M_upstream) 2*cotd(beta)*((M_upstream^2*(sind(beta))^2-1)/(M_upstream^2*(g+cosd(2*beta))+2)) - tand(theta);

val = fsolve(TBM_eq,0.1,option);

end

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Dominic Babula 2023-10-17

Thanks for bringing that to my attention. Considering this, the generated data is expected. I essentially terminated the pcolor plot at M-values >= 10 by setting them to zero, which caused these spikes in value. This was done as the display of larger M-values was not required.

I do not want to display these contours, how would you go about this? Is there a simple way to do it?

Thanks!