How can I use fprintf to print indexes of a matrix?

I'm given a 50x10 matrix "A" of complex numbers and asked to write a program to search it for elements which meet certain criteria. The criteria requires a complex number's complex modulus to fall within +/- 10% of a target value of 5. If the criteria is met, this is a "hit". Each time a hit occurs, formatted data for that element must be stored in a new matrix B, and the information for the hit must be printed to the screen before the program's next iteration. The screen output for each hit should look like this:

where the data printed represent 1) the element's location in A, 2) the complex number (real and imag components), 3) the complex modulus of the complex nunmber, and 4) the phase angle of the complex number.

Here's the code so far:

clc;
close all;
clear all;

% load external data
load matrix_data.mat

% creating variables
i = 1;
j = 1;
k = 1;
pct_diff = 0.1;
targetDiff = .5;
B(1,1) = 0;
hits = 0;


while (i<=50)       % iterates through each row of
    while (j<=10)   % and column of A
        modulusMinus5 = abs(abs(A(i,j))-5) % finds the absolute difference between target value and complex modulus
        if (modulusMinus5<=targetDiff)  % if the criteria is met
            
            B(k,1) = real(A(i,j));  % store the following data in 
            B(k,2) = imag(A(i,j));  % a new matrix "B", which will
            B(k,3) = abs(A(i,j));   % be used later for printing
            B(k,4) = angle(A(i,j)); % data to the screen
            
            k = k+1;    % increment counter k to create a new row in matrix B
            
            % print formatted data each time there's a hit
            fprintf('A(%f,%f) = %f + %f j , r = %f , phi = %f\n', i,j,B(k,1), B(k,2), B(k,3), B(k,4));
        end
        j= j + 1;   % increment j to continue searching the columns in row i
    end
    i = i + 1;  % increment i to search the next column in matrix A
end

i only runs once and doesn't iterate (i=1). j increments 4 times (j = 5 before I get the error). k increments only once (k=2). The error is below:

It looks like the error refers to i, which I want to print to show which row of A the hit was located in.

I've had no success looking for a solution on google. Any help would be greatly appreciated!

Marshall

Answer 1

[Marshall Prince]

Found my main problem! I changed my while loops to for loops and the program now checks each element in A. I now have 37 hits. Thanks for all the help, everyone! You set me on the right track!

Answer 2

[madhan ravi]

B(i,j) not B(k,1)) likewise for the rest

[Mark Sherstan]

Also add your k counter after the fprintf

[madhan ravi]

if B is a matrix that part is not necessary plus the matrix B has to be preallocated before the loop

[Marshall Prince]

"B(i,j) not B(k,1)) likewise for the rest"

So if I do that, and there's a hit in row 1 of A, then it will be stored in row 1 of B, but if there's no hit in row 2 of A, and there is one in row 3 of A, then B will have a hit in its first row, and then B will have an empty 2nd row and a hit in its 3rd row. I created the k counter for this reason to serve only B.

Is there a better way to populate B without creating empty rows in it?

[Marshall Prince]

@madhan ravi,

By preallocating it, do you mean that I need to create B and each of its elements before the loop? If I don't know how many hits I'll get, how can I do that? I'm trying to make sure there are no empty rows in B.

[Marshall Prince]

@ Mark Sherstan,

Thanks for pointing that out about the k counter. Completely overlooked that.

Answer 3

[madhan ravi]

You might also want to look at uniquetol() .

Note: If only your condition is met B gets filled with certain numbers else they are only zeros as per the preallocation , converted your while loops to for loops for conveniency.

clc;
close all;
clear all;
% load external data
load matrix_data.mat
% creating variables
k = 0;
pct_diff = 0.1;
targetDiff = .5;
B=zeros(50,4);  % preallocate
counts=0;
hits = 0;
for i=1:50       % iterates through each row of
    for j=1:10   % and column of A
        modulusMinus5 = abs(abs(A(i,j))-5); % finds the absolute difference between target value and complex modulus
        if abs(modulusMinus5-targetDiff)<=1e-4  % if the criteria is met , you're working with float numbers so add tolerance
            hits = hits + 1;
            B(k,1) = real(A(i,j));  % store the following data in 
            B(k,2) = imag(A(i,j));  % a new matrix "B", which will
            B(k,3) = abs(A(i,j));   % be used later for printing
            B(k,4) = angle(A(i,j)); % data to the screen
                        
            % print formatted data each time there's a hit
            fprintf('A(%f,%f) = %f + %f j , r = %f , phi = %f\n', i,j,B(k,1), B(k,2), B(k,3), B(k,4));
        else 
            counts = counts + 1;  % to know how many times the conditions were not satisfied
        end
    end
            k = k+1;    % increment counter k to create a new row in matrix B %% should be placed between the two loops 
end

After running the code just type k in command window , if you get 50 for k then we are right meaning 50 rows had been touched. Matrix a has 500 elements so counts + hits should result to 500 meaning all the elements were accessed.

[Marshall Prince]

I moved the k counter so if was immediately after the fprintf statement. It's working better now. Here's the output:

My concern now is that it is only checking the first row of A. I found this out by inserting an fprintf statement to show which element of A is being checked with each iteration. Here's the code now:

while (i<50)       % iterates through each row of
    while (j<10)   % and column of A
        
        fprintf('Current Element is (%i,%i)\n', i,j);
        
        modulusMinus5 = abs(abs(A(i,j))-5); % finds the absolute difference between target value and complex modulus
        
        if (modulusMinus5<=targetDiff)  % if the criteria is met
            
            hits = hits + 1;
            
            B(k,1) = real(A(i,j));  % store the following data in 
            B(k,2) = imag(A(i,j));  % a new matrix "B", which will
            B(k,3) = abs(A(i,j));   % be used later for printing
            B(k,4) = angle(A(i,j)); % data to the screen
             
            % print formatted data each time there's a hit
            fprintf('A(%f,%f) = %f + %fj, r = %f, phi = %f\n', i,j,B(k,1), B(k,2), B(k,3), B(k,4));
            
            k = k+1;    % increment counter k to create a new row in matrix B
        end
        j= j + 1;   % increment j to continue searching the columns in row i
    end 
    i = i + 1;  % increment i to search the next column in matrix A
end

And the output:

Any suggestions on this?