http://www.mathworks.com/help/techdoc/ref/fftshift.html
If you check that link - thats what I want to do in the first picture - swap quadrants of a matrix.
However, I cant seem to think of a good way to do this without having several loops to pull out the relevant sub-matrices.
I need it to work with MxN matrices, where M and N can be any combination of even and odd.
Thanks
The following should work
sz = ceil(size(A)/2)
A = A([sz(1)+1:end, 1:sz(1)], [sz(2)+1:end, 1:sz(2)])
That only works for 2d matrices, but can be easily generalized to the Nd case.
If you enter type fftshift.m at MATLAB's command line, you'll see the source code for MATLAB's implementation of the function (use edit fftshift.m if you want to view it in the editor with syntax highlighting). I'm not posting the code here, as it is copyrighted. However, you can try it on your machine and re-implement the same in C. Its up to you to figure out the license terms etc, if you're into any of that.
Related
I have the following function that I wish to solve using fzero:
f = lambda* exp(lambda^2)* erfc(lambda) - frac {C (T_m - T_i)}/{L_f*sqrt(pi)}
Here, C, T_m, T_i, and L_f are all input by the user.
On trying to solve using fzero, MATLAB gives the following error.
Undefined function or variable 'X'.
(where X are the variables stated above)
This error is understandable. But is there a way around it? How do I solve this?
This is answered to the best of my understanding after reading your question as it's not really clear what you are exactly trying and what you want exactly.
Posting the exact lines of code helps a big deal in understanding(as clean as possible, remove clutter). If then the output that matlab gives is added it becomes a whole lot easier to make sure we answer your question properly and it allows us to try it out. Usually it's a good idea to give some example values for data that is to be entered by the user anyway.
First of to make it a function it either needs a handle.
Or if you have it saved it as a matlab file you generally do not want other inputs in your m file then the variable.
So,
function [out]=yourfun(in)
constants=your values; %you can set a input or inputdlg to get a value from the user
out= something something, your lambda thingy probably; %this is the equation/function you're solving for
end
Now since that is not all that convenient I suggest the following
%declare or get your constants here, above the function makes it easier
syms lambda
f = lambda* exp(lambda^2)* erfc(lambda) - frac {C (T_m - T_i)}/{L_f*sqrt(pi)};
hf=matlabFunction(f); %this way matlab automatically converts it to a function handle, alternatively put #(lambda) in front
fzero(hf,x0)
Also this matlab page might help you as well ;)
I am working on some scripts for which I use several functions from the EEGLAB package for matlab. Most of these functions make it possible to surpress the GUI from showing, for example using f( ... 'gui','off'), or by using a different version of the same function. However, I can not figure out how to do this for the function pop_eegfiltnew(). Two similar functions are eegfilt(), which seems to be an outdated version of the function, and firfilt() however, pop_eegfiltnew() has more arguments than these other two, so they are certainly not the same in functional terms.
Anyone knows how to get around this?
If you supply enough arguments to pop_eegfiltnew it does not pop up a GUI.
For example if you wanted to filter your signal 1 Hz highpass you would:
EEG = pop_eegfiltnew(EEG, 1, 0);
This is because the first argument of pop_eegfilt is EEG structure, the second is locutoff (lower edge of the passband) and the third is hicutoff (higher edge of the passband).
I am trying to vectorise a for loop. I have a set of coordinates listed in a [68x200] matrix called plt2, and I have another set of coordinates listed in a [400x1] matrix called trans1. I want to create a three dimensional array called dist1, where in dist1(:,:,1) I have all of the values of plt2 with the first value of trans1 subtracted, all the way through to the end of trans1. I have a for loop like this which works but is very slow:
for i=1:source_points;
dist1(:,:,i)=plt2-trans1(i,1);
end
Thanks for any help.
If I understood correctly, this can be easily solved with bsxfun:
dist1 = bsxfun(#minus, plt2, shiftdim(trans1,-2));
Or, if speed is important, use this equivalent version (thanks to #chappjc), which seems to be much faster:
dist1 = bsxfun(#minus, plt2, reshape(trans1,1,1,[]));
In general, bsxfun is a very useful function for cases like this. Its behaviour can be summarized as follows: for any singleton dimension of any of its two input arrays, it applies an "implicit" for loop to the other array along the same dimension. See the doc for further details.
Vectorizing is a good first optimization, and is usually much easier than going all in writing your own compiled mex-function (in c).
However, the golden middle-way for power users is Matlab Coder (this also applies to slightly harder problems than the one posted, where vectorization is more or less impossible). First, create a small m-file function around the slow code, in your case:
function dist1 = do_some_stuff(source_points,dist1,plt2,trans1)
for i=1:source_points;
dist1(:,:,i)=plt2-trans1(i,1);
end
Then create a simple wrapper function which calls do_some_stuff as well as defines the inputs. This file should really be only 5 rows, with only the bare essentials needed. Matlab Coder uses the wrapper function to understand what typical proper inputs to do_some_stuff are.
You can now fire up the Matlab Coder gui from the Apps section and simply add do_some_stuff under Entry-Point Files. Press Autodefine types and select your wrapper function. Go to build and press build, and you are good to go! This approach usually bumps up the execution speed substantially with almost no effort.
BR
Magnus
I have a project to transform an image using dwt.
I successfully done it using function dwt2, and now I try to use function dwt3 by changes some code from the function dwt2 (add more subband: 8 subbands). Unfortunately, an error comes out, which said "Too many output arguments".
My question is, what is the right way to write MATLAB code for dwt3? Is it not same as dwt2, just add more subbands?
Just by looking at the official documentation for dwt2 and dwt3, I see that dtw3 has only 1 output variable, whereas dtw2 has 4.
I assume you just replaced the string dtw2 in your code to dwt3, without paying attention to the amount of allowed output variables. So there you go, that's where the error "too many output variables" comes from...
If dwt3 only returns the transformed vector, cut the number of output variables to 1, and I'm sure the error will away:
Y = dwt3(X, 'db2');
Here I transformed X using dwt3 with the Daubechies 2-tap wavelet, and stored the result in Y.
P.S
You need to show more code if you want more productive, helpful answers...
I need to calculate Tanimoto Coefficient. I don't know what's wrong in my code. I have 2 nearly similar images. But the value obtained using my code indicates that the two images are highly dissimilar. Kindly help me with my code.
%Tanimoto coeff
I=imread('sliver3.jpg');
J=imread('ref5.jpg');
figure,imshow(I),title('Original');
figure,imshow(J),title('Reference');
inter=intersect(I,J,'rows');
uni=union(I,J,'rows');
si=size(inter);
su=size(uni);
tc=si/su
I attach three images here. First one is the segmented output. Second is a reference image.Third is also a reference but which is highly dissimilar. So, the output must be that, first and second must be nearly similar and first and third must be highly dissimilar. But I'm getting the opposite.
For first two images, tc =0.4895
For first and third images, tc=0.5692
Kindly help me out.
I think you should use the sum() function on union and intersect instead of size() since the Tanimoto Coefficient is the "summation of the intersect"/"summation of the union"