how to distinguish between four zeros in matlab plotting

I ploted the zeros of the function f(z), where z is a complex number and its rootes are complex numbers. for example

When f(z) has 4 zeros move in the complex plane with time t. How can I write the name of these zeros on their graph to show the movement of each zero in the complex plane. (I mean How do I distinguish zeros from each other?) on the graph.

Thank you very much

Answer 1

[Voss]

Something like this?

% get some complex numbers, z:
f = [1 2 3 4 5];
z = roots(f)

z = 
  -1.2878 + 0.8579i
  -1.2878 - 0.8579i
   0.2878 + 1.4161i
   0.2878 - 1.4161i

% plot z on the complex plane and label them as 'Zero #1', etc.:
figure();
x = real(z);
y = imag(z);
for ii = 1:numel(z)
    plot(x(ii),y(ii),'ko');
    hold on
    text(x(ii),y(ii),sprintf('Zero #%d',ii), ...
        'VerticalAlignment','top','HorizontalAlignment','center');
end

[Aisha Mohamed]

Hi Dear

Thank you very much this answer is work, could you please let me know how can I write (zeta) instead of zero in the figure ? because when I wrote:

text(x(ii),y(ii),sprintf('\zeta #%d',ii), ...

zeta did not appeare in the figure?

I will appreciate any help

Thank you.

[Voss]

@Aisha Mohamed Because the "\zeta" is part of the first argument to sprintf (i.e., the string format specification), the backslash will be treated as a special character for sprintf. In order to avoid that and just have the backslash be a backslash, so that it is correctly interpreted as "\zeta" by the text function, use a double-backslash to tell sprintf to ignore the backslash. It looks like this:

% get some complex numbers, z:
f = [1 2 3 4 5];
z = roots(f);
% plot z on the complex plane and label them as 'Zero #1', etc.:
figure();
x = real(z);
y = imag(z);
for ii = 1:numel(z)
    plot(x(ii),y(ii),'ko');
    hold on
    text(x(ii),y(ii),sprintf('\\zeta #%d',ii), ...
        'VerticalAlignment','top','HorizontalAlignment','center');
end

Here's the result from sprintf in both cases, for your reference:

sprintf('\zeta #%d',3) % \z doesn't mean anything to sprintf

Warning: Escaped character '\z' is not valid. See 'doc sprintf' for supported special characters.

ans =

  1×0 empty char array

sprintf('\\zeta #%d',3) % \\ becomes \ (so that \\zeta becomes \zeta, which is then used in text())

ans = '\zeta #3'