I've tried to search stackoverflow for a solution, but the cases I found differ slightly from what I'm trying to do, so I thought I'd ask.
I have a loop in MATLAB, which for every iteration, a large matrix is computed. I want to save each matrix as a separate MAT file, however each file needs to be named according to its position in loop. For example: matrix1, matrix2,...
The method I'm using to save my data (which seemed different from the few examples I found) is the following (where matrix is the generated matrix and matrix1 is the filename to be saved for the matrix corresponding to i = 1)
save matrix1 matrix;
I've seen something similar to
save ['matrix', i] matrix;
But I can't seem to remember the exact syntax.
Sorry if the question is very basic, a simple nod in the right direction for this type of saving would be greatly appreciated.
Use the functional form of save:
save(['matrix', int2str(i)], 'matrix');
Here's my nod:
eval(['save matrix' num2str(i) ' matrix;']);
Good luck! :)
Related
I am receiving a text file with 1000 matrices of size 2x2 each day from someone, in the following format (only 3 matrices are shown here instead of 1000):
0.96875000 0.03125000
0.03125000 0.96875000
0.96875000 0.01562500
0.03125000 0.98437500
0.99218800 0.03125000
0.00781250 0.96875000
I need to make a 2x2x1000 array in MATLAB. Ideally I could do something simple like:
[0.96875000 0.03125000
0.03125000 0.96875000;
0.96875000 0.01562500
0.03125000 0.98437500;
0.99218800 0.03125000
0.00781250 0.96875000]
After reading the MATLAB documentation on multidimensional arrays and the MATLAB documentation for the cat function, I figured out that I could make the required array in the following way (the first argument of cat is 3 because I'm concatenating the 2x2 matrices along the 3rd dimension):
cat(3,...
[0.96875000 0.03125000
0.03125000 0.96875000],...
[0.96875000 0.01562500
0.03125000 0.98437500],...
[0.99218800 0.03125000
0.00781250 0.96875000])
But that does not work if I put spacing between the lines as in my "ideal" example above, and the need for all the commas and dots makes it a bit uglier in my opinion.
While writing this question, I have discovered that I can run my "ideal" example and then use reshape, which I prefer over my solution using the cat function. For this, I don't even need the semi-colons. However Cris Luengo correctly pointed out in the comments that reshape is not enough and permute is also needed, and then Luis Mendo pointed out in chat that the solution is not so simple:
permute(reshape(ideal.',2,2,[]),[2 1 3])
Andras Deak has done what we thought was impossible, which is to remove the transpose, but the solution is still quite complicated, and was not easy to engineer:
permute(reshape(ideal,2,[],2),[1 3 2])
Ideally one would not need to use cat or reshape to make a 3D array, when the original data is already so nicely formatted in what the human eye can already see is a 3D array of several 2x2 matrices.
Is there a simpler way to build the 3D array in MATLAB using the data in the format I have?
So far I have done the following on my own:
Searched online and found the above two MATLAB documentation articles which lead me to the above solution using cat
Came up with the above solution using reshape while writing this question, then it got improved by Cris and Luis in the comments and chat 😊.
Also: I tried saving the data in a .txt file and clicked import in MATLAB, knowing that the import GUI gives some options for how the data is to be organized in the resulting MATLAB array, but there did not seem to be any option to make this a 3D array.
Indeed there is no "direct" way to import this text as a 3D matrix. This is the easiest way I can come up with:
Save the input as a .txt file
Use the import tool (Import Data button in the Variable toolbar) to import the data as a Mx2 matrix. Choose "Numeric Matrix" as "Output Type". And you can "exclude rows with" "blank cells" to avoid the empty rows.
Besides reshape() and permute(), using cell array to format it as below might be more intuitive and less error prone to someones.
% The number of 2x2 matrices
N = size(m,1)/2;
% Split each 2x2 matrix into a cell
c = mat2cell(m, 2*ones(1,N), 1);
% Concatenate along the 3rd dimension
output3DMatrix = cat(3, c{:});
I have a very huge 3D matrix, the data was written into disk for future use. Writing the matrix into a bin is easy, reading it back however have some issue.
Write to bin:
z=repmat(complex(rand(5),rand(5)),[1 1 5])
z_imag = imag(z);
z_real = real(z);
adjacent = [z_real z_imag];
fileID = fopen('complex.bin','w');
fwrite(fileID,adjacent,'double')
And now, I try to read it back using memmapfile:
m = memmapfile('complex.bin', 'Offset', 0, 'Format', {'double' [5,5,5] 'x'});
complexValues = complex(m.Data(:).x(1,:), m.Data(:).x(2,:)); %this line doesn't work though, just for explanation's sake
It gave me an error saying that
Error using memmapfile/subsref (line 764) A subscripting operation on
the Data field attempted to create a comma-separated list. The
memmapfile class does not support the use of comma-separated lists
when subscripting.
I was referring to the solution here, the suggested solution used the reshape to shape the matrix beforehand (as contrast to my method above). I try to avoid using reshape in my code as I'm dealing with very huge data and that might computationally expensive and takes a long time. Is there an alternative/better way to do this?
Thanks in advance!
Unfortunately I am not too tech proficient and only have a basic MATLAB/programming background...
I have several csv data files in a folder, and would like to make a histogram plot of all of them simultaneously in order to compare them. I am not sure how to go about doing this. Some digging online gave a script:
d=dir('*.csv'); % return the list of csv files
for i=1:length(d)
m{i}=csvread(d(i).name); % put into cell array
end
The problem is I cannot now simply write histogram(m(i)) command, because m(i) is a cell type not a csv file type (I'm not sure I'm using this terminology correctly, but MATLAB definitely isn't accepting the former).
I am not quite sure how to proceed. In fact, I am not sure what exactly is the nature of the elements m(i) and what I can/cannot do with them. The histogram command wants a matrix input, so presumably I would need a 'vector of matrices' and a command which plots each of the vector elements (i.e. matrices) on a separate plot. I would have about 14 altogether, which is quite a lot and would take a long time to load, but I am not sure how to proceed more efficiently.
Generalizing the question:
I will later be writing a script to reduce the noise and smooth out the data in the csv file, and binarise it (the csv files are for noisy images with vague shapes, and I want to distinguish these shapes by setting a cut off for the pixel intensity/value in the csv matrix, such as to create a binary image showing these shapes). Ideally, I would like to apply this to all of the images in my folder at once so I can shift out which images are best for analysis. So my question is, how can I run a script with all of the csv files in my folder so that I can compare them all at once? I presume whatever technique I use for the histogram plots can apply to this too, but I am not sure.
It should probably be better to write a script which:
-makes a histogram plot and/or runs the binarising script for each csv file in the folder
-and puts all of the images into a new, designated folder, so I can sift through these.
I would greatly appreciate pointers on how to do this. As I mentioned, I am quite new to programming and am getting overwhelmed when looking at suggestions, seeing various different commands used to apparently achieve the same thing- reading several files at once.
The function csvread returns natively a matrix. I am not sure but it is possible that if some elements inside the csv file are not numbers, Matlab automatically makes a cell array out of the output. Since I don't know the structure of your csv-files I will recommend you trying out some similar functions(readtable, xlsread):
M = readtable(d(i).name) % Reads table like data, most recommended
M = xlsread(d(i).name) % Excel like structures, but works also on similar data
Try them out and let me know if it worked. If not please upload a file sample.
The function csvread(filename)
always return the matrix M that is numerical matrix and will never give the cell as return.
If you have textual data inside the .csv file, it will give you an error for not having the numerical data only. The only reason I can see for using the cell array when reading the files is if the dimensions of individual matrices read from each file are different, for example first .csv file contains data organised as 3xA, and second .csv file contains data organised as 2xB, so you can place them all into a single structure.
However, it is still possible to use histogram on cell array, by extracting the element as an array instead of extracting it as cell element.
If M is a cell matrix, there are two options for extracting the data:
M(i) and M{i}. M(i) will give you the cell element, and cannot be used for histogram, however M{i} returns element in its initial form which is numerical matrix.
TL;DR use histogram(M{i}) instead of histogram(M(i)).
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 not a very hardcore coder in MATLAB, i have learned every thing from youtube and books. This might be a very simple question but i do not know what search for answer.
In MATLAB i am trying to do something like this.
>>[a,b,c] = [1,2,3]
and i want output like this.
>> a = 1
b = 2
c = 3
So Bsically question is that : - User will define the matrix of variables([a,b,c]) in staring of code and during process of the code similar matrix will be displayed and as input a matrix will be asked([1,2,3]). I dont know how do this without writing a loop code in which i will take every single variable from variable matrix and save the value in that variable by eval function.
well above written code is wrong and i know, i can do this with "for" loop and "eval" function.
but problem is that no. of variables(a,b,c) will never be constant and i want know if there exist any in built function or method in MATLAB which will work better than a for loop.
As i told earlier i don't know what to search for such a problem and either this is a very common question.
Either way i will be happy if you can at least tell me what to search or redirect me to a related question.
Please do write if you want any more information or for any correction.
Thank you.
The deal function can do this for a fixed number of inputs:
[A,B,C]=deal(1,2,3)
If you don't know how many inputs you will get beforehand, you have to do some fooling around. This is what I've come up with:
V=[1,2,3,4,5,6,7]
if length(V)>1
for i=1:length(V)
S{i}=['A' num2str(i)];
G{i}=['V(' num2str(i) ')'];
end
T=[S{1} ','];
R=[G{1} ','];
for i=2:length(V)-1
T=[T S{i} ','];
R=[R G{i} ','];
end
T=[T S{length(V)}];
R=[R G{length(V)}];
eval(['[' T ']=deal(' R ')'])
else
A1=V
end
But then dealing with A1, ... , An when you don't know how many there are will be a pain!
This is somehow known as "tuple unpacking" (at least it's what I would search in python!). I could find this thread which explains that you could do this in Octave (I checked and it works in Matlab also). You have to transform the vector into a cell array before:
values = num2cell([1,2,3])
[a,b,c] = values{:}