You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gui_cor.m
    path of file: ./repos/HRTF-Individualization/model/matlabcode/gui/anthro
    
    the code of the file until where you have to start completion: function varargout = gui_cor(varargin)
% GUI_COR M-file for gui_cor.fig
%      GUI_COR, by itself, creates a new GUI_COR or raises the existing
%      singleton*.
%
%      H = GUI_COR returns the handle to a new GUI_COR or the handle to
%      the existing singleton*.
%
%      GUI_COR('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in GUI_COR.M with the given input arguments.
%
%      GUI_COR('Property','Value',...) creates a new GUI_COR or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      
    
function plotsurface(hObject, eventdata, handles)
global azimuth_angles
global elevation_angles
global DATA_COR
global data_text


az_val = get(handles.azimuth,'Value');
el_val = get(handles.elevation,'Value');

pc_val1 = get(handles.pcnr1,'Value');
pc_val2 = get(handles.pcnr2,'Value');

azimuth_real = azimuth_angles(az_val);
elevation_real = elevation_angles(el_val);

text = sprintf('Correlation between %s No.%i of Azimuth (%d), Elevation (%2.3f) and %s No.%i of all other positions',data_text,pc_val1,azimuth_real,elevation_real,data_text,pc_val2);

axes(handles.axes1)
cla;

% visualize only more than 0.75%
if (get(handles.cor,'Value') ==1)
DATA_COR_1 = DATA_COR;
DATA_COR_1(find(DATA_COR_1<0.75))=0;
surface(elevation_angles,azimuth_angles,DATA_COR_1);
%surface(DATA_COR_1);
% visualize all data
else
surface(elevation_angles,azimuth_angles,DATA_COR);
end