# I want to colour the area between red line and black line below the intersection point. how am i going to do it?

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I want to colour the area between red line and black line below the intersection point. how am i going to do it?
c=[3,5];
A=[1,2;1,1;0,1];
b=[2000;1500;600];
y1=0:1:max(b);
x21=(b(1)-A(1,1)*y1)./A(1,2);
x22=(b(2)-A(2,1)*y1)./A(2,2);
x23=(b(3)-A(3,1)*y1)./A(3,2);
plot(y1,x21,'r',y1,x22,'k',y1,x23,'b');
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### Answers (2)

Chunru on 28 Nov 2021
c=[3,5];
A=[1,2;1,1;0,1];
b=[2000;1500;600];
y1=0:1:max(b);
x21=(b(1)-A(1,1)*y1)./A(1,2);
x22=(b(2)-A(2,1)*y1)./A(2,2);
x23=(b(3)-A(3,1)*y1)./A(3,2);
plot(y1,x21,'r',y1,x22,'k',y1,x23,'b');
hold on
fill( [y1(end:-1:993)'; y1(993:end)'; ], [x22(end:-1:993)'; x21(993:end)'], 'y' )
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Star Strider on 28 Nov 2021
Use ‘logical indexing’ to identify & fill the appropriate area —
c=[3,5];
A=[1,2;1,1;0,1];
b=[2000;1500;600];
y1=0:1:max(b);
x21=(b(1)-A(1,1)*y1)./A(1,2);
x22=(b(2)-A(2,1)*y1)./A(2,2);
x23=(b(3)-A(3,1)*y1)./A(3,2);
figure
plot(y1,x21,'r',y1,x22,'k',y1,x23,'b');
hold on
Lv = x21 >= x22; % Logical Index To Selecet Vector Segments
patch([y1(Lv) flip(y1(Lv))], [x21(Lv) flip(x22(Lv))], 'g') % Use 'Lv' With 'patch' To Fill The Required Region
hold off
This approach can easily be used to fill other areas of the plot, as required. This requires one indexing line to create ‘Lv’ and one patch call.
.
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