Why are my plots for K values and initial conditions all the same colour even with hold on

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Connor McLaughlin
Connor McLaughlin 2023-10-31
编辑： Voss 2023-10-31
% Mesh Grid in (Diamtoms(D),Zooplankton(P))-plane
[D, P] = meshgrid(-0.8:1:10, -0.8:1:10);
% Parameters
hold on
for K=1:10;
s=1;
e=1;
r=1;
H=1;
d=0.75;
% System as a 2-D function
f = @(t,X) [X(1)*(r*(1-X(1)*(1/K))-(s*X(1)/1+s*H*X(1))*X(2));
X(2)*(e*(s*X(1))/(1+s*H*X(1))-d)];
%Direction Filed
% Ddot is dD/dt and Pdot is dP/dt derivatives
Ddot = D-(1./K).*D.*D-(s*D)./((1+s.*H.*D)).*P;
Pdot = P.*((s.*D)./(1+s.*H.*D))-P.*d;
% Vector Field
figure(1)
quiver(D,P,Ddot,Pdot,'k','LineWidth',1.5)
timespan=[0 100];
% Phase Trajectories
X0=0.5*K*rand;Y0=K*rand;
[ts, Xs] = ode45(f,timespan, [X0, Y0]);
% plot of several trajectories
plot(Xs(:,1), Xs(:,2),'k', 'Linewidth', 2)
xlabel('Prey, D', 'FontSize',14)
ylabel('Predator, P', 'FontSize',14)
set(gca, 'FontSize', 16)
xlim([-0.8 10])
ylim([-0.8 10])
end
  1 个评论
Beñat Arribas
Beñat Arribas 2023-10-31
The 'k' defines the color of the plots, which is equivalent to black color. Removing this will turn between the different colors set by default.
quiver(D,P,Ddot,Pdot,'k','LineWidth',1.5)
plot(Xs(:,1), Xs(:,2),'k', 'Linewidth', 2)

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采纳的回答

Voss
Voss 2023-10-31
Ran in:
They are all the same color because you have specified them all to be black when you plotted them. The 'k' means black in, e.g.:
quiver(D,P,Ddot,Pdot,'k','LineWidth',1.5)
% ...
plot(Xs(:,1), Xs(:,2),'k', 'Linewidth', 2)
Removing the 'k' gives lines with different colors:
% Mesh Grid in (Diamtoms(D),Zooplankton(P))-plane
[D, P] = meshgrid(-0.8:1:10, -0.8:1:10);
% Parameters
hold on
for K=1:10;
s=1;
e=1;
r=1;
H=1;
d=0.75;
% System as a 2-D function
f = @(t,X) [X(1)*(r*(1-X(1)*(1/K))-(s*X(1)/1+s*H*X(1))*X(2));
X(2)*(e*(s*X(1))/(1+s*H*X(1))-d)];
%Direction Filed
% Ddot is dD/dt and Pdot is dP/dt derivatives
Ddot = D-(1./K).*D.*D-(s*D)./((1+s.*H.*D)).*P;
Pdot = P.*((s.*D)./(1+s.*H.*D))-P.*d;
% Vector Field
figure(1)
quiver(D,P,Ddot,Pdot, 'LineWidth',1.5)
timespan=[0 100];
% Phase Trajectories
X0=0.5*K*rand;Y0=K*rand;
[ts, Xs] = ode45(f,timespan, [X0, Y0]);
% plot of several trajectories
plot(Xs(:,1), Xs(:,2), 'Linewidth', 2)
xlabel('Prey, D', 'FontSize',14)
ylabel('Predator, P', 'FontSize',14)
set(gca, 'FontSize', 16)
xlim([-0.8 10])
ylim([-0.8 10])
end
  1 个评论
Voss
Voss 2023-10-31
Ran in:
Also, you can move those things that don't depend on the value of the variable K out of the for loop:
% Mesh Grid in (Diamtoms(D),Zooplankton(P))-plane
[D, P] = meshgrid(-0.8:1:10, -0.8:1:10);
% Parameters
s=1;
e=1;
r=1;
H=1;
d=0.75;
timespan=[0 100];
Pdot = P.*((s.*D)./(1+s.*H.*D))-P.*d;
figure(1)
hold on
for K=1:10;
% System as a 2-D function
f = @(t,X) [X(1)*(r*(1-X(1)*(1/K))-(s*X(1)/1+s*H*X(1))*X(2));
X(2)*(e*(s*X(1))/(1+s*H*X(1))-d)];
%Direction Filed
% Ddot is dD/dt and Pdot is dP/dt derivatives
Ddot = D-(1./K).*D.*D-(s*D)./((1+s.*H.*D)).*P;
% Vector Field
quiver(D,P,Ddot,Pdot, 'LineWidth',1.5)
% Phase Trajectories
X0=0.5*K*rand;Y0=K*rand;
[ts, Xs] = ode45(f,timespan, [X0, Y0]);
% plot of several trajectories
plot(Xs(:,1), Xs(:,2), 'Linewidth', 2)
end
xlabel('Prey, D', 'FontSize',14)
ylabel('Predator, P', 'FontSize',14)
set(gca, 'FontSize', 16)
xlim([-0.8 10])
ylim([-0.8 10])

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更多回答（1 个）

Les Beckham
Les Beckham 2023-10-31
Ran in:
Because you told Matlab to make all of the lines black.
For example, the 'k' in this command means "make the lines black":
plot(Xs(:,1), Xs(:,2),'k', 'Linewidth', 2)
% Mesh Grid in (Diamtoms(D),Zooplankton(P))-plane
[D, P] = meshgrid(-0.8:1:10, -0.8:1:10);
% Parameters
% hold on
s=1;
e=1;
r=1;
H=1;
d=0.75;
for K=1:10;
% System as a 2-D function
f = @(t,X) [X(1)*(r*(1-X(1)*(1/K))-(s*X(1)/1+s*H*X(1))*X(2));
X(2)*(e*(s*X(1))/(1+s*H*X(1))-d)];
%Direction Filed
% Ddot is dD/dt and Pdot is dP/dt derivatives
Ddot = D-(1./K).*D.*D-(s*D)./((1+s.*H.*D)).*P;
Pdot = P.*((s.*D)./(1+s.*H.*D))-P.*d;
% Vector Field
figure(1)
quiver(D,P,Ddot,Pdot) % <<< removed color and linewidth specification
hold on % <<< hold on AFTER first plot command
timespan=[0 100];
% Phase Trajectories
X0=0.5*K*rand;
Y0=K*rand;
[ts, Xs] = ode45(f,timespan, [X0, Y0]);
% plot of several trajectories
plot(Xs(:,1), Xs(:,2)) % <<< removed color and linewidth specification
xlabel('Prey, D', 'FontSize',14)
ylabel('Predator, P', 'FontSize',14)
set(gca, 'FontSize', 16)
xlim([-0.8 10])
ylim([-0.8 10])
end

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