How do I put annotation text pointing towards specific coordinate?

Below is my code , I have tried to put annotation text pointing towards a coordinate(3.4, 4.8248) using trial and error method . What is the proper way ?

x=[1 2 2.5 3 4 5]

x = 1×6

1.0000 2.0000 2.5000 3.0000 4.0000 5.0000

y=[0 5 7 6.5 2 0]

y = 1×6

0 5.0000 7.0000 6.5000 2.0000 0

A=3.4;Lagrange(x,y,A)

A = 3.4000

s = 0

c = 1×2 cell array
    {[3.4000]}    {[4.8248]}

ans = 4.8248

function yint=Lagrange(x,y,xx)
A=3.4
n=length(x);
s=0
for i=1:n
    product=y(i);
    for j=1:n
        if i~=j
            product=product*(xx-x(j))/(x(i)-x(j));
        end
    end
    s=s+product;
   
end


yint=s;
figure()
plot(x,y)
hold on
scatter(A,yint,"x","b")
scatter(x,y,"o")
title('Lagrange Interpolation'); xlabel('x'); ylabel('f(x)');
c={A yint}
annotation('textarrow',[0.7 0.6],[0.7 0.64],'String',c)
hold off
legend('Interpolated Function','Result Point f(3.4)','Given Data');
hold off

end

Answer 1

[Matt J]

x=[1 2 2.5 3 4 5];
y=[0 5 7 6.5 2 0];
A=3.4;Lagrange(x,y,A);

function yint=Lagrange(x,y,xx)
A=3.4;
n=length(x);
s=0;
for i=1:n
    product=y(i);
    for j=1:n
        if i~=j
            product=product*(xx-x(j))/(x(i)-x(j));
        end
    end
    s=s+product;
   
end


yint=s;
figure()
plot(x,y)
hold on
scatter(A,yint,"x","b")
scatter(x,y,"o")
title('Lagrange Interpolation'); xlabel('x'); ylabel('f(x)');
c={A yint};

%%%%%Matt J added
ax=gca;
xl=xlim; 
yl=ylim;

xy0=[xl(1),yl(1)];
Dxy=[diff(xl),diff(yl)];

fn=@(xy) (xy(:)'-xy0)./Dxy.*ax.InnerPosition([3,4])+ax.InnerPosition([1,2]);
p=fn([3.4, 4.8248]);
%%%%%%

annotation('textarrow',[0.7 p(1)],[0.7 p(2)],'String',c)
hold off
legend('Interpolated Function','Result Point f(3.4)','Given Data');
hold off

end

[Samson David Puthenpeedika]

Oh thankyou ..understood now

[Star Strider]

I like ‘fn’ and the supporting code!

+1

.

Answer 2

[Sulaymon Eshkabilov]

Here you can use the values of c to place where you want your annotation to be displayed along with the arrow. E.g.:

...
c={A yint}
annotation('textarrow',[c{1,1}, c{1,1}-0.07*max(x)]/max(x),[c{1,2},c{1,2}-0.07*max(y)]/max(y),'String',c)
...

[Samson David Puthenpeedika]

Still it is showing the same result . No difference

[Matt J]

Sulaymon Eshkabilov's comment moved here

WIth the proposed solution, you don't need to find the coordinates by a trial and error. It takes up the found values of c. In other words, the annotation placement changes with respect to the calculated values of c.

[Samson David Puthenpeedika]

How to use values of c in the above code? When i tried values of 'c' it was giving error that values should be between 0-1