I think this is vectorizing

Given: Write a code that prompts user to enter a number of rows and columns. Create a matrix, with the provided size that has random integers between -10 and 10.

Find: How do I have MATLAB individually look at each value in the matrix and determine if the value is negative, and if it is, add one to a variable used to keep track of the negative values? (Otherwise do nothing). Then display to the user the number of negative values in the matrix.

Issue: I am running into syntax error brain. In my head this code works, but it's not what MATLAB thinks is right.

My solution: Once I figure out how to get my random numbers to properly generate I can tackle the tracking system... I might be going about this all wrong, though.

R=input('Enter the number of rows: ');
C=input('Enter the number of columns: ');
MAT=[R(randi([-10,10]),C(randi([-10,10])))]; % Getting an error here, syntax?
for x=1:R<1
    disp('Negative')
        for y=1:C<1
            disp('Negative')
        end
end
% Then create a variable neg and somehow??? do neg=neg+1 every time there is a
% negative value found in the above for loop.

Answer 1

[Venkat Siddarth Reddy]

Hi Kyle,

In the above code you are trying to use the variables "R" and "C" as the functions to create a matrix of dimensions of R and C. However, these are not functions but variables with user-defined values.

To create a matrix of random numbers of above dimensions you can pass the dimension values to the "randi" function itself.

%Let the values of R,C be 3,4
R=3;
C=4;
MAT= randi([-10 10],R,C)

MAT = 3x4

4 -3 0 -7 -7 -9 -5 3 7 4 -7 -8

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And to find the count of negative numbers.You can either loop through each element of the matrix and check for the value or you can apply a boolean matrix operations and count for all the valid elements. Following example shows both the methods

%Method-1 Iterate through each element

negCount=0;
for i=1:R
    for j=1:C
        if(MAT(i,j)<0)
            negCount=negCount+1;
        end
        
    end
end
negCount

negCount = 7

%Method-2 Matrix boolean operation
%Generating a boolean matrix on condition whether the element is less than zero or not. 

negCount=nnz(MAT<0)  %nnz - gives number of non zero elements in the matrix.

negCount = 7

To learn more about randi with these arguments and nnz function, refer to the following documentation:

• https://www.mathworks.com/help/matlab/ref/nnz.html
• https://www.mathworks.com/help/matlab/ref/randi.html?s_tid=doc_ta#buf2dpy-7

I hope it helps!.

[Spaceman]

Eureka! Of course, this makes complete sense. I normally code after going to classes all morning and working 9 hours, so I'm often pretty mentally and physically exhausted by the time I get around to practicing. But this makes complete sense now that I see it. I was unsure if I could state 2 for loops before I passed it an if statement. Thank you!