The msgbox pops up here, but when I click OK, the graph doesn't appear. Why?

hm = msgbox('To calibrate pick up three non-collinear points');
waitfor(hm)

X = ones(3, 3); 
S = zeros(3, 2); 

prompt = {'Enter actual angle value, deg',...
'Enter actual lever value, m'};
numlines = 2; defaultanswer = {'', ''};
options.Resize = 'on';
options.WindowsStyle = 'normal';
options.Interpreter = 'tex';
for k = 1:3
[ xs, ys ] = ginput(1);
S(k, 1) = xs;
S(k, 2) = ys;
name = [ 'Point ' num2str(k) ];
Actual = inputdlg(prompt, name, numlines, defaultanswer, options);
X(k, 1) = str2double(Actual{1});
X(k, 2) = str2double(Actual{2});
end
C = X\S;
hm = msgbox('Start digitizing from zero to maximum heel');
waitfor(hm)
DIG = ones(2, 1); % initialize array of coordinates of the
% digitized points
l = 1; % initialize counter of digitized points
button = 'Yes'; % initialize loop sentinel
while strcmp(button, 'Yes')
[ xd, yd ] = ginput(1);
plot(xd, yd, 'r.') % mark digitized point
DIG(1, l) = xd;
DIG(2, l) = yd;
l = l+ 1;
qstring = [ 'Digitize point ' num2str(l) ];
button = questdlg(qstring, 'Digitizing');
end
hold off

[ m, n ] = size(DIG);
REAL = zeros(2, n); % allocate space for real-world
% coordinates of digitized points
A2 = C(1:2,:)'; C2 = C(3, :)'*ones(1, n); B2 = DIG - C2;

REAL = A2\B2; % returns real-world coordinates of
% digitized points
phi = REAL(1, :); % real-word heel-angle values, degrees
phi(1) = 0;
GZ = REAL(2, :); % real-world righting-lever values
GZ(1) = 0;
phir = pi*phi/180; % real-world heel-angle values, radians

phii = 0: 2.5: max(phi); % axis for spline interpolation
GZi = spline(phi, GZ, phii); % interpolated values

l = length(GZi); GZl = GZi(1: (l-1)); S1 = [ 0 cumsum(GZl) ];
GZ2 = GZi(2: l); S2 = [ 0 cumsum(GZ2) ]; S = (pi*2.5/(2*180))*(S1 + S2);


% Choose mode of entering GM
LS = [ {'Numerical value of GM known'},...
{'GM to be picked up on graph'},...
{'GM unknown'} ];
[ Selection, ok ] = listdlg('Liststring', LS, 'SelectionMode','Single'); 
switch Selection
case 1
% begin arguments of input dialogue
prompt = {'Enter GM value in m'};
numlines = 1;
defaultanswer = {''};
options.Resize = 'on';
options.WindowsStyle = 'normal';
options.Interpreter = 'tex';
% end arguments of input dialogue
GMstring = inputdlg(prompt, name, numlines, defaultanswer, options);
GM = str2double(GMstring);
case 2
[ xd, yd ] = ginput(1);
Bgm = [ xd; yd ] - C(3, :)';
GMphi = A2\Bgm; % returns real-world coordinates
GM = GMphi(2);
case 3
GM = 0;
end


figure(2) = ploty(phii, GZi, phii, S);
if GM > 0
    hold on
    axis([ 0 1.1*max(phii) 0 1.1*GM ])
    t = [ 'GM = ' num2str(GM) ' m' ];
    text(185/pi, GM, t)
    hold off
end

title([ 'Curves of statical and dynamical stability for file ' filename ])
xlabel('Heel angle, deg')
set(get(Ax(1), 'Ylabel'),'String','Lever arms, m')
set(get(Ax(2),'Ylabel'),'String','Area under curve, m \cdot rad')

SSCURVE = GZi;
AREAS = S;
fid = fopen('scdigitizer.out', 'w');
fprintf(fid, 'Curves of statical and dynamical stability\n');
fprintf(fid, 'calculated with the function SCDIGITIZER\n');
fprintf(fid, 'for file %s \n', filename);
fprintf(fid, ' Heel angle GZ Area\n');
fprintf(fid, ' Degrees m m.rad\n');
for k = 1:l
fprintf(fid, '%10.1f %10.2f %10.3f \n', phii(k), GZi(k), S(k));
end
fclose(fid)

and

The msgbox pops up here, but when I click OK, the graph doesn't appear. Why?

function [ SSCURVE, AREAS ] = scdigitizer(filename)
if nargin < 1
[ filename, pathname ] = uigetfile({'*.jpg'; '*.gif'; '*.bmp'; '*.tif'},...
'Select a graphic input file');
end
A = imread(filename);
him = image(A); 
axis off 

grid
hold on

And if I add this code at the beginning, when I save it as a MATLAB code file, I can't see anything in the selection window when I run it. What should I do?

Answer 1

[Image Analyst]

You forgot to say

hold on

after your first call to plot() so, because of that, each point you plot blows away the prior point you plotted.