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# Ahmed A. Selman

Active since 2013

Ph.D. in theoretical nuclear physics, author of four books and lecturer at the College of Science-University of Baghdad since 2008. Interested with image processing applications in astronomy mainly. I begun using Matab since the year 2000 (I think it was ver.5.), and still there is much to learn about.
Professional Interests: Theoretical Physics

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Help naming text file according to user input
Just add the extension you like to the variable (fileName), as prompt = 'Please enter the file name: '; fileName = input(...

8 years ago | 4

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how to find the second order partial derivative of an image?
See older and similar question here: <http://www.mathworks.com/matlabcentral/answers/67893>

8 years ago | 0

Reshape array for 256 by 256 matrix showing 16 by 256

8 years ago | 0

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Save 512x512 matrix to text file
This code works perfectly. To check it add the following at the very end of the above code: fid = fopen('Mymatrix.txt','r'...

8 years ago | 0

solve 2 equation of 2 unknown
Use the code instead: clc clear syms theta3 r1 %sind(theta3) % NOT NEEDED r2=3; r3=3.927; r4=0.335; ...

8 years ago | 1

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extracting submatrices from cell
Try the same example with: X={1, 'a'; 'b', 3.14}; K1=X(2,:) [K21 K22]=X{2,:} Then use whos to...

8 years ago | 0

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How to identify boundaries of shapes in an image using the change in color
There are few files in the file-exchange <http://www.mathworks.com/matlabcentral/fileexchange/> so do some search there, you mig...

8 years ago | 0

error message using polynom
A polynomial P(x) is said to be (badly conditioned) when a small variances of x leads to large errors of P, causing unstable err...

8 years ago | 0

Creating a matrix with matrices on the sub and super diagonals
Use the command (diag) for creating a (main) diagonal matrix from a vector A, and the command (spdiags) to create sub- and super...

8 years ago | 0

Picking out a value from a Vector in a Loop iteration
Within your same code: ... plot(Y(:,1),Y(:,2),'o'); z=zeros(1,length(X)); % Add this for i = 1:length(X) f...

8 years ago | 0

More help with probability...
Just pay attention to how you use function call inside a program. Either you have two files as stated above, or use one main (ca...

8 years ago | 0

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How to plot with a logarithmic scale?
semilogx(x,y)

8 years ago | 2

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how to solve loops conditions ??
#1) Using for loops only: clear k=0; for i=1:6 for j=1:5 k=k+1; A(i,j)=k; end end ...

9 years ago | 0

Symbolic expressions: abs(x^(1/3)) =?= abs(x)^(1/3)
Some times we get confused between mathematics and programming, it is an often thing. Yet, mathematics means logic, programs try...

9 years ago | 0

how to write a .dat file in matlab?
The obvious method is to construct a loop to read filenames, inside it, open and read, then accumulate the data content in some ...

9 years ago | 0

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Reading many files in one loop

9 years ago | 0

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How to read a text file line by line?
Try selecting one dimension a time for each line, e.g., ... time=fscanf(fID,'%g',[1 1:2:inf]); acce=fscanf(fID,'%g',[...

9 years ago | 0

Obtaning a matrix with the right indexes
Try this out to see if it solves the issue: clear clc N=20; %for example H=sym(zeros(N,4)); B=1:N; ...

9 years ago | 0

How to create a nested for loop to create a mesh plot
I'm not sure what are your conditions (in the if statements), but you used (y1) as a matrix index which cannot be made unless (y...

9 years ago | 0

If all variables other than (y) are known, then let's write some notes here: 1) Try to first define the variables, namely: kw...

9 years ago | 0

Issue with writing multiple variable to excel sheet
It is not practical to write a single line in an excel file, for a large amount of data or inside a long-time running loop. If y...

9 years ago | 1

while loop question number 2
In such a case, using a while loop cannot do the job, but an if statement can. So, I think this is what are you looking for (con...

9 years ago | 0

How to plot a complicated function
It is the same code you wrote, only add loops over c and tau, and use the function (ezplot) to plot a function handle. And DO NO...

9 years ago | 0

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how to code probability in general??
First what is magic(2)? I thought the smallest magic matrix comes (3-by-3) since Magic (2) doesn't satisfy the condition (sum ea...

9 years ago | 0

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Lighting the Solar System - Omnidirectional light source (Sun)
I don't know really if Matlab is used for such tasks, but haven't you tried Simulink for easier handling of the problem? Such gr...

9 years ago | 0

while loop in data file for trapz?
Apparently, the variable (Num) is not (1). That's why the (while loop) returns nothing. I've tried the lines you posted and it w...

9 years ago | 0

Switch columns in a matrix without a loop
for exchanging two columns 3 - 9 : A = randi(20,4,10); % A random 4 by 10 matrix of integers A(1,:)=[1 2 3 4 5 6 7 ...

9 years ago | 0

I WANT TO SOLVE THE EQUATION for x: x*exp(x)=(a1-x)*a2*a3 . Here a1 and a3 are matrices and a2 is a constant. I cant solve the equation using solve
True, indeed. Not only for (A,B) = (11,13) and (3,-6), but for a wide range of other set, including the given coefficients.....

9 years ago | 0

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