参考链接

代码分为两个：绘图代码与magnify.m

绘图代码就是普通的绘图代码，以下为例

%https://zhuanlan.zhihu.com/p/655767542
clc
clear
close all
x = 0:pi/100:2*pi;
y1 = sin(x);
plot(x,y1,'r-o');
hold on
y2=sin(x)-0.05;
y3=sin(x)+0.05;
xlim([0 2*pi]);
ylim([-1.5 1.5]);
plot(x,y2,'b-v');
plot(x,y3,'m-.');
legend('线型1','线型2','线型3','Location','northeast')

运行该m文件后运行magnify.m（magnify.m与绘图代码放在同一文件夹下）
magnify.m

%https://zhuanlan.zhihu.com/p/655767542
function magnify(f1)
warning off
%
%magnify(f1)
%
%  Figure creates a magnification box when under the mouse
%  position when a button is pressed.  Press '+'/'-' while
%  button pressed to increase/decrease magnification. Press
%  '>'/'<' while button pressed to increase/decrease box size.
%  Hold 'Ctrl' while clicking to leave magnification on figure.
%
%  Example:
%     plot(1:100,randn(1,100),(1:300)/3,rand(1,300)), grid on,
%     magnify;% Rick Hindman - 7/29/04if (nargin == 0), f1 = gcf; end;
set(f1, ...'WindowButtonDownFcn',  @ButtonDownCallback, ...'WindowButtonUpFcn', @ButtonUpCallback, ...'WindowButtonMotionFcn', @ButtonMotionCallback, ...'KeyPressFcn', @KeyPressCallback);
return;function ButtonDownCallback(src,eventdata)f1 = src;a1 = get(f1,'CurrentAxes');a2 = copyobj(a1,f1);set(f1, ...'UserData',[f1,a1,a2], ...'Pointer','fullcrosshair', ...'CurrentAxes',a2);set(a2, ...'UserData',[2,0.2], ...  %magnification, frame size'Color',get(a1,'Color'), ...'Box','on');xlabel(''); ylabel(''); zlabel(''); title('');set(get(a2,'Children'), ...'LineWidth', 2);set(a1, ...'Color',get(a1,'Color')*0.95);set(f1, ...'CurrentAxes',a1);ButtonMotionCallback(src);
return;function ButtonUpCallback(src,eventdata)H = get(src,'UserData');f1 = H(1); a1 = H(2); a2 = H(3);set(a1, ...'Color',get(a2,'Color'));set(f1, ...'UserData',[], ...'Pointer','arrow', ...'CurrentAxes',a1);if ~strcmp(get(f1,'SelectionType'),'alt'),delete(a2);end;
return;function ButtonMotionCallback(src,eventdata)H = get(src,'UserData');if ~isempty(H)f1 = H(1); a1 = H(2); a2 = H(3);a2_param = get(a2,'UserData');f_pos = get(f1,'Position');a1_pos = get(a1,'Position');[f_cp, a1_cp] = pointer2d(f1,a1);set(a2,'Position',[(f_cp./f_pos(3:4)) 0 0]+a2_param(2)*a1_pos(3)*[-1 -1 2 2]);a2_pos = get(a2,'Position');set(a2,'XLim',a1_cp(1)+(1/a2_param(1))*(a2_pos(3)/a1_pos(3))*diff(get(a1,'XLim'))*[-0.5 0.5]);set(a2,'YLim',a1_cp(2)+(1/a2_param(1))*(a2_pos(4)/a1_pos(4))*diff(get(a1,'YLim'))*[-0.5 0.5]);end;
return;function KeyPressCallback(src,eventdata)H = get(gcf,'UserData');if ~isempty(H)f1 = H(1); a1 = H(2); a2 = H(3);a2_param = get(a2,'UserData');if (strcmp(get(f1,'CurrentCharacter'),'+') | strcmp(get(f1,'CurrentCharacter'),'='))a2_param(1) = a2_param(1)*1.2;elseif (strcmp(get(f1,'CurrentCharacter'),'-') | strcmp(get(f1,'CurrentCharacter'),'_'))a2_param(1) = a2_param(1)/1.2;elseif (strcmp(get(f1,'CurrentCharacter'),'<') | strcmp(get(f1,'CurrentCharacter'),','))a2_param(2) = a2_param(2)/1.2;elseif (strcmp(get(f1,'CurrentCharacter'),'>') | strcmp(get(f1,'CurrentCharacter'),'.'))a2_param(2) = a2_param(2)*1.2;end;set(a2,'UserData',a2_param);ButtonMotionCallback(src);end;
return;% Included for completeness (usually in own file)
function [fig_pointer_pos, axes_pointer_val] = pointer2d(fig_hndl,axes_hndl)
%
%pointer2d(fig_hndl,axes_hndl)
%
%  Returns the coordinates of the pointer (in pixels)
%  in the desired figure (fig_hndl) and the coordinates
%       in the desired axis (axes coordinates)
%
% Example:
%  figure(1),
%  hold on,
%  for i = 1:1000,
%     [figp,axp]=pointer2d;
%     plot(axp(1),axp(2),'.','EraseMode','none');
%     drawnow;
%  end;
%  hold off% Rick Hindman - 4/18/01if (nargin == 0), fig_hndl = gcf; axes_hndl = gca; end;
if (nargin == 1), axes_hndl = get(fig_hndl,'CurrentAxes'); end;set(fig_hndl,'Units','pixels');pointer_pos = get(0,'PointerLocation');  %pixels {0,0} lower left
fig_pos = get(fig_hndl,'Position');  %pixels {l,b,w,h}fig_pointer_pos = pointer_pos - fig_pos([1,2]);
set(fig_hndl,'CurrentPoint',fig_pointer_pos);if (isempty(axes_hndl)),axes_pointer_val = [];
elseif (nargout == 2),axes_pointer_line = get(axes_hndl,'CurrentPoint');axes_pointer_val = sum(axes_pointer_line)/2;
end

运行后直接在原figure框中右键需要放大的地方即可弹出子图
此时按住邮件不放并按住Ctrl键和+键/-键可放大/缩小子图