I need help for drawing a constraint in Matlab in 2D

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nadia nadi
nadia nadi 2025-3-7
评论： nadia nadi 2025-3-9
Ran in:
Dear All,
I'm trying to draw a set of constraints but I got a wrong line for the constraint 2x1<=3 !!!! I need a vertical line !! I approciate any help from you !!!
Many Thanks,
Nadia
clear;clc;close;
%max 5x1+7x2;
%3x1+8x2<=12;
%x1+x2<=2;
%2x1<=3;
%x2<=4;
%x1,x2>=0;
%% plot the feasible region %Generate data
[x1,x2] = meshgrid(0:0.1:10);% i changed 0.1 to 0.01 to plot the fourth constraint
NB=5*x1+7*x2;
% Get True where condition applies, false where not.
cond1=3*x1+8*x2<=12; cond2=x1+x2<=2; cond3=2*x1<=3; cond4=x2<=2;
% Get boundaries of the condition
p1=(12-3*x1(1,:))/8;
p2=2-x1(1,:);
p3=3/2-x1(1,:);
p4=2-x2(1,:);
%Delete Areas whereCondition does not apply;
NB(~cond1)=NaN; NB(~cond2)=NaN; NB(~cond3)=NaN; NB(~cond4)=NaN;
%% Plot
[x2,h]=contourf(x1,x2,NB,0); % command contourf for filling the area between the contour levels
hold on
plot(x1(1,:),p1,'r','LineWidth',2); text(x1(1,20),p1(20), '\leftarrow Cond1'); %arbitrary location
plot(x1(1,:),p2,'k','LineWidth',2); text(x1(1,15),p2(15), '\leftarrow Cond2'); %arbitrary location
plot(x1(1,:),p3,'b','LineWidth',2); text(x1(1,20),p3(20), '\leftarrow Cond3'); %arbitrary location
plot(x1(1,:),p4,'b','LineWidth',2); text(x1(1,20),p4(20), '\leftarrow Cond3'); %arbitrary location
axis([0 5 0 5])
xlabel('x1')
ylabel('x2')
●
  3 个评论
显示 1更早的评论
Sam Chak
Sam Chak 2025-3-7

Woukd you also like to apply a colorful gradient translucent patch on the bounded feasible region as well?

nadia nadi
nadia nadi 2025-3-9

I’m ok thank you very much I’m appreciate your help.

Best

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采纳的回答

Sam Chak
Sam Chak 2025-3-7
编辑：Sam Chak 2025-3-7
Ran in:
Hi @nadia nadi
You should replace the p3 line with this:
p3 = 3/2*ones(1, numel(x1(1,:)));
...
plot(p3, x1(1,:))
clear;clc;close;
%max 5x1+7x2;
%3x1+8x2<=12;
%x1+x2<=2;
%2x1<=3;
%x2<=4;
%x1,x2>=0;
%% plot the feasible region %Generate data
[x1,x2] = meshgrid(0:0.01:10);% i changed 0.1 to 0.01 to plot the fourth constraint
NB=5*x1+7*x2;
% Get True where condition applies, false where not.
cond1=3*x1+8*x2<=12; cond2=x1+x2<=2; cond3=2*x1<=3; cond4=x2<=2;
% Get boundaries of the condition
p1=(12-3*x1(1,:))/8;
p2=2-x1(1,:);
% p3=3/2-x1(1,:);
p3 = 3/2*ones(1, numel(x1(1,:)));
p4=2-x2(1,:);
%Delete Areas whereCondition does not apply;
NB(~cond1)=NaN; NB(~cond2)=NaN; NB(~cond3)=NaN; NB(~cond4)=NaN;
%% Plot
[x2,h]=contourf(x1,x2,NB,0); % command contourf for filling the area between the contour levels
hold on
plot(x1(1,:),p1,'r','LineWidth',2); text(x1(1,20),p1(20), '\leftarrow Cond1'); %arbitrary location
plot(x1(1,:),p2,'k','LineWidth',2); text(x1(1,15),p2(15), '\leftarrow Cond2'); %arbitrary location
plot(p3,x1(1,:),'b','LineWidth',2); text(x1(1,20),p3(20), '\leftarrow Cond3'); %arbitrary location
plot(x1(1,:),p4,'b','LineWidth',2); text(x1(1,20),p4(20), '\leftarrow Cond3'); %arbitrary location
axis([0 5 0 5])
xlabel('x1')
ylabel('x2')

更多回答（1 个）

Rik
Rik 2025-3-7
Ran in:
I have no clue what you mean mathematically with what you wrote, but if you want to plot a vertical line, you can use xline():
x=linspace(0,2*pi);
plot(x,sin(x))
xline(pi)
yline(-0.5*sqrt(2))
legend({'data','xline','yline'})

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