MATLAB: How to get a program to display something from a function

displayfunction

Is there a way to display something from a function when running a program?

Best Answer

Remove the semicolon at the end of

counter = counter + 1

The value of 'counter' will then display every time it's updated.

A more visually appealing method is to use fprintf

count = counter + 1; 
fprintf('count = %d\n', count);

Related Solutions

MATLAB: Something wrong with quat2angle() function

I agree that this looks like a bug, and you should submit a bug report to TMW for this. I ran it in R2017a and R2020a and both versions have the bug. I first started with this post:

https://www.mathworks.com/matlabcentral/answers/244488-quat2angle-function?s_tid=srchtitle

I modified that code to use your 'ZYX' and 'XYZ' rotation sequences for q = [0.5 0.5 0.5 0.5], and I compared that result to the results of a conversion to direction cosine matrix and a quaternion rotation multiply. The 'ZYX' matched but the 'XYZ' didn't. Hence I conclude that it is a bug in the quat2angle( ) function. If you perturb the quaternion slightly (use a small value for f, e.g. 1e-10) it gets the correct result. But it can't handle that exact quaternion properly. The code I used for this is:

disp('------------------------------')
disp('quat2angle( ) test')
% sample data
f = 1e-10; % Use 0 here to demonstrate quat2angle bug
q = [0.5 0.5 0.5 0.5] + (rand(1,4)*2-1)*f;
q = q / norm(q)
vi = [1 2 3]';
% quat2angle ZYX
disp('------------------------------')
disp('dcm = quat2dcm(q)')
dcm = quat2dcm(q)
[a3,a2,a1] = quat2angle(q,'ZYX');
c = cos(a3);
s = sin(a3);
r3 = [ c  s  0;
      -s  c  0;
       0  0  1];
c = cos(a2);
s = sin(a2);
r2 = [ c  0 -s;
       0  1  0;
       s  0  c];
c = cos(a1);
s = sin(a1);
r1 = [ 1  0  0;
       0  c  s;
       0 -s  c];
disp('dce = result of individual rotation matrix multiplies, ZYX')
dce = r1 * r2 * r3
% compare rotation methods

vb = dcm * vi;
ve = dce * vi;
vq = quatmultiply(quatconj(q),[0 vi']);
vq = quatmultiply(vq,q);
vr = quatrotate(q,vi');
disp('------------------------------')
disp('vi = input inertial vector')
disp(vi')
disp('vb = dcm * vi')
disp(vb')
disp('ve = dce * vi')
disp(ve')
disp('vq = conj(q) * vi * q')
disp(vq(2:4))
disp('vr = quatrotate(q,vi'')')
disp(vr)
disp('q')
disp(q);
disp('angle2quat(angles) for ZYX')
disp(angle2quat(a3,a2,a1,'ZYX'))
disp('------------------------------')
% quat2angle XYZ
disp('------------------------------')
[a3,a2,a1] = quat2angle(q,'XYZ');
c = cos(a3);
s = sin(a3);
r3 = [ 1  0  0;
       0  c  s;
       0 -s  c];
c = cos(a2);
s = sin(a2);
r2 = [ c  0 -s;
       0  1  0;
       s  0  c];
c = cos(a1);
s = sin(a1);
r1 = [ c  s  0;
      -s  c  0;
       0  0  1];
disp('dce = result of individual rotation matrix multiplies, XYZ')
dce = r1 * r2 * r3
% compare rotation methods
vb = dcm * vi;
ve = dce * vi;
vq = quatmultiply(quatconj(q),[0 vi']);
vq = quatmultiply(vq,q);
vr = quatrotate(q,vi');
disp('------------------------------')
disp('vi = input inertial vector')
disp(vi')
disp('vb = dcm * vi')
disp(vb')
disp('ve = dce * vi')
disp(ve')
disp('vq = conj(q) * vi * q')
disp(vq(2:4))
disp('vr = quatrotate(q,vi'')')
disp(vr)
disp('q')
disp(q);
disp('angle2quat(angles) for XYZ')
disp(angle2quat(a3,a2,a1,'XYZ'))
disp('------------------------------')

And the results I get for f=0 are:

>> quat2angle_test
------------------------------
quat2angle( ) test
f =
     0
q =
    0.5000    0.5000    0.5000    0.5000
------------------------------
dcm = quat2dcm(q)
dcm =
     0     1     0
     0     0     1
     1     0     0
dce = result of individual rotation matrix multiplies, ZYX
dce =
    0.0000    1.0000         0
   -0.0000    0.0000    1.0000
    1.0000   -0.0000    0.0000
------------------------------
vi = input inertial vector
     1     2     3
vb = dcm * vi
     2     3     1
ve = dce * vi
     2     3     1
vq = conj(q) * vi * q
     2     3     1
vr = quatrotate(q,vi')
     2     3     1
q
    0.5000    0.5000    0.5000    0.5000
angle2quat(angles) for ZYX
    0.5000    0.5000    0.5000    0.5000
------------------------------
------------------------------
dce = result of individual rotation matrix multiplies, XYZ
dce =
    0.0000         0   -1.0000
         0    1.0000         0
    1.0000         0    0.0000
------------------------------
vi = input inertial vector
     1     2     3
vb = dcm * vi
     2     3     1
ve = dce * vi
   -3.0000    2.0000    1.0000
vq = conj(q) * vi * q
     2     3     1
vr = quatrotate(q,vi')
     2     3     1
q
    0.5000    0.5000    0.5000    0.5000
angle2quat(angles) for XYZ
    0.7071         0    0.7071         0
------------------------------

You can see the discrepancy in the dcm produced and the different quaternion produced by angle2quat when using the 'XYZ' rotation sequence. There may be other quaternion and sequence combinations that produce erroneous errors for edge cases also.

When you perturb the q slightly (small non-zero f = 1e-10), things work correctly:

>> quat2angle_test
------------------------------
quat2angle( ) test
f =
   1.0000e-10
q =
    0.5000    0.5000    0.5000    0.5000
------------------------------
dcm = quat2dcm(q)
dcm =
    0.0000    1.0000   -0.0000
   -0.0000    0.0000    1.0000
    1.0000   -0.0000    0.0000
dce = result of individual rotation matrix multiplies, ZYX
dce =
    0.0000    1.0000   -0.0000
   -0.0000    0.0000    1.0000
    1.0000   -0.0000    0.0000
------------------------------
vi = input inertial vector
     1     2     3
vb = dcm * vi
    2.0000    3.0000    1.0000
ve = dce * vi
    2.0000    3.0000    1.0000
vq = conj(q) * vi * q
    2.0000    3.0000    1.0000
vr = quatrotate(q,vi')
    2.0000    3.0000    1.0000
q
    0.5000    0.5000    0.5000    0.5000
angle2quat(angles) for ZYX
    0.5000    0.5000    0.5000    0.5000
------------------------------
------------------------------
dce = result of individual rotation matrix multiplies, XYZ
dce =
    0.0000    1.0000         0
   -0.0000         0    1.0000
    1.0000   -0.0000    0.0000
------------------------------
vi = input inertial vector
     1     2     3
vb = dcm * vi
    2.0000    3.0000    1.0000
ve = dce * vi
    2.0000    3.0000    1.0000
vq = conj(q) * vi * q
    2.0000    3.0000    1.0000
vr = quatrotate(q,vi')
    2.0000    3.0000    1.0000
q
    0.5000    0.5000    0.5000    0.5000
angle2quat(angles) for XYZ
    0.5000    0.5000    0.5000    0.5000
------------------------------

MATLAB: Changing pictures

Define "automatically." Do you mean in a for loop? See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F so you'll know how to do stuff like this:

filePattern = fullfile(myFolder, '*.jpg');
jpegFiles = dir(filePattern);
for k = 1:length(jpegFiles)
  baseFileName = jpegFiles(k).name;
  fullFileName = fullfile(myFolder, baseFileName);
  fprintf(1, 'Now reading %s\n', fullFileName);
  imageArray = imread(fullFileName);
  imshow(imageArray);  % Display image.
  drawnow; % Force display to update immediately.
    promptMessage = sprintf('Do you want to Continue or Cancel?');
    button = questdlg(promptMessage, 'Continue', 'Continue', 'Cancel', 'Continue');
    if strcmpi(button, 'Cancel')
    break;
    end
end

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Related Solutions

MATLAB: Something wrong with quat2angle() function

MATLAB: Changing pictures

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