Matlab Coding Display Help

I have this code:

function [A] = Gauss_Elim(A)
%Performs Gaussian Elimination%
N = length(A);
tol = 1e-6;
%for each pivot along the diagonal
for ii = 1:N-1
    %for each row under the pivot
    for jj=ii+1:N
        if abs(A(jj,ii)) > tol
            
            %factor is ratio between pivot value
            %and entry below pivot in row jj
            fac=A(ii,ii)/A(jj,ii);
            
            %row replacement
            A(jj,:) = fac*A(jj,:)-A(ii,:);
            
        end
    end
end
end

This code produces the correct answer, but how would I display the steps the code takes to get the correct answer?

Answer 1

[Dave B]

Do you mean you would like to see what's in A on each iteration? Here's 4-5 ways depending on how complicated you want it to be (I'll just do the full code and run it for the last one!)

• You can remove the ; at the end of the line

A(jj,:) = fac*A(jj,:)-A(ii,:)

• You can add the line disp(A)

A(jj,:) = fac*A(jj,:)-A(ii,:);
disp(A)

• You could show it graphically by adding a call to imagesc on each iteration of the loop

A(jj,:) = fac*A(jj,:)-A(ii,:);
imagesc(A) % consider specifying CLim on the axes, as this will be changing on each iteration...

• For the image solution, you might consider storing the (step-wise) output of A so that you can play the movie again later, or write it to a video file, etc.

function [B,A] = Gauss_Elim(A)
...
B=nan(N,N,sum(1:N)+1);
cnt=1;
for ii = 1:N-1
    ...
    A(jj,:) = fac*A(jj,:)-A(ii,:);
    B(:,:,cnt)=A;
    cnt=cnt+1;
    ...

• You could plot each step into a separate subplot (this could get slow if you have a large matrix)

Gauss_Elim(rand(10))

ans = 10×10

0.3995 0.4408 0.4586 0.4269 0.1814 0.0349 0.4339 0.6469 0.4362 0.6070 0 -0.3572 -0.1512 -0.1629 -0.1583 0.0285 -0.4141 -0.3145 -0.0164 -0.5157 0 0 -0.1919 0.1574 -0.0239 0.5764 0.3408 0.4011 0.2645 -0.1513 0 0 0 0.7394 0.1896 0.2065 1.1101 0.4552 -1.9977 1.2333 -0.0000 0 0 0 -0.9684 1.1577 -0.3696 1.7478 3.2485 -1.8617 0.0000 0 0 0 0.0000 -5.2155 -0.2409 -1.6482 -7.9881 3.7745 -0.0000 0 0 0 -0.0000 0 0.1991 0.1445 0.2797 0.4623 -0.0000 0 0 0 -0.0000 0 -0.0000 -1.9966 -2.5243 -5.4185 -0.0000 0 -0.0000 0.0000 -0.0000 0 0.0000 0.0000 17.8712 1.0736 0.0000 0 0.0000 -0.0000 0.0000 0 0.0000 -0.0000 0 28.2920

function [A] = Gauss_Elim(A)
    t=tiledlayout('flow');
    colormap turbo
    %Performs Gaussian Elimination%
    N = length(A);
    tol = 1e-6;
    %for each pivot along the diagonal
    for ii = 1:N-1
        %for each row under the pivot
        for jj=ii+1:N
            if abs(A(jj,ii)) > tol
                
                %factor is ratio between pivot value
                %and entry below pivot in row jj
                fac=A(ii,ii)/A(jj,ii);
                %row replacement
                A(jj,:) = fac*A(jj,:)-A(ii,:);
                imagesc(nexttile,A)
                clims=get(t.Children,'CLim');
                if iscell(clims)
                    clims=cell2mat(get(t.Children,'CLim'));
                end
                caxis([min(clims(:,1)) max(clims(:,2))])
                drawnow
            end
        end
    end
end

[Nick]

Yes, sorry I meant to display the matrix A on each iteration. Thank you for the help!

Answer 2

[Image Analyst]

To show each step (each line of code as it's being executed), you can tell it

echo on

To show A, remove the semicolon from the end of the line.

A(jj,:) = fac*A(jj,:)-A(ii,:)