Is it possible to plot rows of a matrix without a for loop?

Question

I have a matrix that stores multiple functions in its rows each evaluated against the interval [0,20]. I'm running through a for loop to output them at the moment. Is there a better way of doing this or is this the only way of doing it in MATLAB?

h = 0.1;
xLine = 0:h:20;
nGrid = length(xLine);

nu = [ 1, 2, 3 ];
nNu = length(nu);

b = zeros(nNu,nGrid);
for i=1:nNu
    b(i:i,1:nGrid) = besselj(nu(i), xLine);
end

hFig = figure(1);
hold on
set(hFig, 'Position', [1000 600 800 500]);
for i=1:nNu
    plot(xLine, b(i:i,1:nGrid))
end

plot(YourMatrix(:,1:end)) for each column and plot(YourMatrix(1:end,:)) for each row. — GameOfThrows
– GameOfThrows, Commented Dec 11, 2015 at 9:23

rayryeng · Accepted Answer · 2015-12-11 09:39:21Z

4

You can use plot vectorized. Specifically, you can supply b directly into plot but you need to make sure that the larger of the two dimensions in b matches the total number of elements in the vector xLine. This is what you have, so we're good. Therefore, because each unique signal occupies a row in your matrix, just supply b into your plot call and use it a single time.

hFig = figure(1);
hold on
set(hFig, 'Position', [1000 600 800 500]);
plot(xLine, b);

This will plot each row as a separate colour. If you tried doing this, you'll see that the plots are the same in comparison to the for loop approach.

Check out the documentation for plot for more details: http://www.mathworks.com/help/matlab/ref/plot.html

edited Dec 11, 2015 at 9:39

answered Dec 11, 2015 at 9:24

rayryeng

105k22 gold badges201 silver badges206 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Ron Ronson Over a year ago

Very nice thanks! I was wondering is there also a nicer way of filling the matrix b? Is there a way of specifying just the row to fill or do I have use the full indexing notation b(i:i,1:nGrid) =?

rayryeng Over a year ago

@Riggs You're welcome! Unfortunately the first parameter has to be a scalar and so you need to use a loop...yup...sucks. However, you can shorten the loop to just do this: for i = 1:nNu, b(i,:) = besselj(nu(i), xLine); end. It's slightly shorter, but it does the same trick. You don't need to do i:i. That's superfluous. Just use i by itself. Also, instead of 1:nGrid, just use :. xLine has nGrid elements, so the output will implicitly be nGrid elements long.

Matthew Gunn · Accepted Answer · 2015-12-11 09:41:18Z

2

Replace for loop with:

plot(xLine, b(:,1:nGrid))

Note: I can't perfectly recall but some older versions of Matlab may want everything in columns and you'd want to transpose the matrices:

plot(xLine.', b(:,1:nGrid).')

edited Dec 11, 2015 at 9:41

answered Dec 11, 2015 at 9:33

Matthew Gunn

4,5291 gold badge15 silver badges31 bronze badges

2 Comments

rayryeng Over a year ago

My comment was nonsense. It looks like that column stuff I talked about has changed. This is good. +1.

Matthew Gunn Over a year ago

@rayryeng Probably good style though to transpose b for compatibility.

Collectives™ on Stack Overflow

Is it possible to plot rows of a matrix without a for loop?

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related