# How can I fill between two curves, but only when one curve is above the other?

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Hello,
I'd like to fill the gap between two lines, but only when one line is above the other.
With the data file attached and the command:
plot(x,y1,'k',x,y2,'k:');
hold on;
xlim([x(1) x(end)]);
jbfill(x',y1',y2',[.8 .8 .8],'none',0,.5);
legend('y1','y2');
hold off;
I can plot:
which always fills the gap between y1 and y2. But I'd like it to be filled only when y1>y2.
Any help on this is very welcome.
Best,

Alex Mcaulley on 26 Jul 2019
You can do a little trick:
plot(x,y1,'k',x,y2,'k:');
hold on;
xlim([x(1) x(end)]);
y1tmp = y1;
y1tmp(y1<y2) = y2(y1<y2);
jbfill(x',y1tmp',y2',[.8 .8 .8],'none',0,.5);
legend('y1','y2');
hold off;

#### 1 Comment

Luciano Campos on 26 Jul 2019
Thanks Alex, this works perfectly!
Best,

KSSV on 26 Jul 2019
plot(x,y1,'k',x,y2,'k:');
hold on;
xlim([x(1) x(end)]);
% jbfill(x',y1',y2',[.8 .8 .8],'none',0,.5);
legend('y1','y2');
hold off;
idx = y1>y2 ;
figure
X = [x(idx) ; flipud(x(idx))] ;
Y = [y1(idx) ; flipud(y2(idx))] ;
fill(X,Y,'r')

Hi, I am new to MATLAB - I just started doing an online course a few weeks ago - so this is probably not a very good solution.
But it works!
plot(x,y1,'k',x,y2,'k:');
hold on;
xlim([x(1) x(end)]);
% initiate temporary variable
temp1 = zeros(1,numel(x));
temp2 = zeros(1,numel(x));
for i = 1:numel(x)
if y1(i) > y2(i)
temp1(i) = y1(i) % only store values of y1 if y1>y2
temp2(i) = y2(i) % only store values of y2 if y1>y2
end
end
jbfill(x',temp1,temp2,[.8 .8 .8],'none',0,.5); % only plot values when y1>y2
legend('y1','y2');
hold off;
shg