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how do i include the one point in the complex plane in my legend

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martinkjr
martinkjr on 23 Oct 2016
Commented: martinkjr on 23 Oct 2016
Hi all
im plotting gershgorin discs for eigenvalues with the following function
% gerschdisc.m
%
% This function plots the Gershgorin Discs for the matrix A passed as an argument.
% It will also plot the centers of such discs, and the actual eigenvalues
% of the matrix.
function gershdisc(A)
A = [sqrt(-1) sqrt(2); sqrt(2) sqrt(-1)];
error(nargchk(nargin,1,1));
if size(A,1) ~= size(A,2)
error('Matrix should be square');
return;
end
% For each row, we say:
for i=1:size(A,1)
% The circle has center in (h,k) where h is the real part of A(i,i) and
% k is the imaginary part of A(i,i) :
h=real(A(i,i)); k=imag(A(i,i));
% Now we try to compute the radius of the circle, which is nothing more
% than the sum of norm of the elements in the row where i != j
r=0;
for j=1:size(A,1)
if i ~= j
r=r+(norm(A(i,j)));
end
end
% We try to make a vector of points for the circle:
N=256;
t=(0:N)*2*pi/N;
% Now we're able to map each of the elements of this vector into a
% circle:
plot( r*cos(t)+h, r*sin(t)+k ,'-');
% We also plot the center of the circle for better undesrtanding:
hold on;
plot( h, k,'+');
end
% For the circles to be better graphed, we would like to have equal axis:
axis equal;
% Now we plot the actual eigenvalues of the matrix:
ev=eig(A);
for i=1:size(ev)
rev=plot(real(ev(i)),imag(ev(i)),'ro');
end
hold off;
legend(rev,'Actual Eigenvalues',,'+');
xlim([-3 3]);
ylim([-3 3]);
end
how do i include the center point and the circle in the legend?

Accepted Answer

dpb
dpb on 23 Oct 2016
Save the handles when you plot them--
...
hLCirc=plot(r*cos(t)+h, r*sin(t)+k ,'-');
hold on;
hLCntr=plot(h, k,'+');
...
legend([hLCirc hLCntr rev],'Circle','Center','Actual Eigenvalues',,'+');
See
doc legend % for more concise ways to write the legend text w/ cellstr arrays, etc., ...

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