Plot uses columns to plot a square matrix, but I need it by rows.
plot(matrix(1:end,1:end), 1:columns)
works great when matrix is rectangular (plots each line of matrix with a different color), but when matrix is square is plots by column (as the documentation clearly states)
I don't want to break the command to a loop because then I will have to specify the color for each line plot.
Is there a way to change the plot defaults to prefer row in square matrices?
You can use a trick and add a line of NaN at the end of the array:
matrix(end+1,:) = NaN;
And now matrix is rectangular, but the NaN won't be displayed during plot.
Best,
Related
I have 2 matrices. Matrix A contains values between 0 and 1 and matrix B contains values between 0 and 90. I would like to display an image with a different color for the numbers in each matrix.
When I use the colormap function with:
figure; colormap(jet); imshow(A);
The image displayed has several levels of gray, when I am supposed to have several colors (because I am using jet).
When I use the colormap function with:
figure; colormap(jet); imshow(B);
The image displayed is completely white, probably because my values are higher than 64 (which is the max of jet).
How can I solve these two problems? I read a lot of tutorials in several forums but I can't find the answer...
Thank you very much for answering my problem!
Just normalize the matrix by its max value if the values are more than 1. So for your B matrix try:
imshow(B/max(B(:)))
You can specify the colormap scaling and the number of actual colors within the colormap like so:
figure; imshow( A, [0 1], 'Colormap', jet(100) );
figure; imshow( B, [0 100], 'Colormap', jet(100) );
The jet(100) indicates 100 unique colors within the colormap to be used.
You are using the wrong function for the task in hand.
imshow expects an N by M by 3 array input, of the RGB channels of an image. When you use a 2D matrix the function assumes it's a grayscale image (it's like replicating it to 3 identical matrices to create these three channels - if all the channels in RGB have the same values you get grayscale colors). You can use this function together with a colormap to get a colored matrix, but there are much more convenient alternatives.
One simple function for getting a colored representation of a matrix is imagesc or (image if you want to scale the values by yourself). This function takes the values in your matrix, and assign them a color from the colormap you choose:
A = rand(10);
figure; colormap(jet); imagesc(A);
Another option is pcolor, which works a little different but give a similar result. pcolor attach the values to the vertices of the cells (in oppose to the center, as imagesc does), and interpolate the color in each cell from its' vertices. The resulted colored matrix is always smaller in one row and one column because it takes n+1 points (values in the original matrix) to define n gaps (the cells in the colored matrix). Here is an example:
A = rand(10);
figure; colormap(jet); pcolor(A);
shading flat
if I have a 2x2 Matrix such as
1 2
4 7
And I want to plot a histogram based on the condition that the diagonals should be the color green, and everything else except the diagonals should be red, how do I do that in Matlab.
I have tried separating the 2x2 matrix into two different vectors representing the diagonal and the others (except diagonals), but when I do:
hist(diagonals)
hist(others)
It doesn't really work and seems to just randomly color code things into one histogram (I do want just the one histogram though.) How do I do this correctly?
Found a solution to my problem, using hold on fixes this issue
histogram(diagonals, 'FaceColor', 'g')
hold on
histogram(others, 'FaceColor', 'r')
hold on
I want to create a 3x3 matrix of plots in MATLAB where each element is a subplot of some corresponding 1000 samples (suppose values are stored in a 3x3x1000 matrix A). I want the subplots to be spaced very close together, and the y axis numbers/labels to only show up for the left subplots and the x axis numbers/labels to only show up for the bottom subplots.
For example, something similar to plotmatrix, except subplot ij would plot A(i,j,:).
plotmatrix example
Is there an easy way to do this in MATLAB? Thanks!
The axes properties of the subplots can be modified to achieve this, but an easier way would be to use a FEX submission called panel. Have a look at its example output:
subplot can do that for you in MATLAB.
h = subplot(3,3,1)
Will split the current figure in a 3 x 3 matrix and creates an axes(area where you plot something) in the 1st cell of the matrix. h is the "handle" to the axes which you can then use to modify the xlabels and ylabels in any way.
Documentation for subplot
Documentation for Axes
I have a matrix M, 135*191*121 double and want to plot it in 3D volume by using those 121 slices. How can I do this? (I need a grayscale image)
Regards
Check out vol3d v2 , it an update to Joe Conti's vol3d function, allowing voxel colors and alpha values to be defined explicitly. In cases where voxels can be any RGB color, use:
vol3d('CData', cdata);
where cdata is an MxNxPx3 array, with RGB color along the 4th dimension. In cases where color and alpha values are highly independent, specify an MxNxP alphamatte as follows:
vol3d('CData', cdata, 'Alpha', alpha);
if you have 3 arrays, storing (x,y,z) coordinates of every point that you need to plot, then you can use function plot3
From matlab help
PLOT3 Plot lines and points in 3-D space.
PLOT3() is a three-dimensional analogue of PLOT().
PLOT3(x,y,z), where x, y and z are three vectors of the same length,
plots a line in 3-space through the points whose coordinates are the
elements of x, y and z.
PLOT3(X,Y,Z), where X, Y and Z are three matrices of the same size,
plots several lines obtained from the columns of X, Y and Z.
Various line types, plot symbols and colors may be obtained with
PLOT3(X,Y,Z,s) where s is a 1, 2 or 3 character string made from
the characters listed under the PLOT command.
PLOT3(x1,y1,z1,s1,x2,y2,z2,s2,x3,y3,z3,s3,...) combines the plots
defined by the (x,y,z,s) fourtuples, where the x's, y's and z's are
vectors or matrices and the s's are strings.
Example: A helix:
t = 0:pi/50:10*pi;
plot3(sin(t),cos(t),t);
PLOT3 returns a column vector of handles to lineseries objects, one
handle per line. The X,Y,Z triples, or X,Y,Z,S quads, can be
followed by parameter/value pairs to specify additional
properties of the lines.
for 3d plots you may also want to look into surf function
I have been trying to figure out how to "hide" the useless part of the triangular matrix from my 3d plot in Matlab.
I have tried drawing a mesh just above that part of the graph with
'EdgeAlpha', 1, 'FaceAlpha', 1,'FaceColor','w','EdgeColor','none'
but it does not help. How should I do it instead?
The only method the semi-worked is using the color scale, but it did not work all the way, plus I need the black and white eps's, which will show the color as black even if it looks white originally...
This is my last hope ;)
Barbara
Short answer: replace "useless" data with the value nan because MATLAB does not plot data values that are nan.
Inserting nan values into the other half of the matrix should do the trick. See the example below - it's clunky, but should give the idea. I chose to multiply by nan, which I attained as shown, but there are half a dozen other things that came to mind.
% Create random data for illustration
data = tril(rand(50));
% I chose to divide by a lower triangular ones matrix (zeros above the
% diagonal) to get nan above the diagonal and ones below
nan_above_diag_ones_below = 1./tril(ones(50,50));
% Plot data with and without hiding the "useless part"
figure,
subplot(1,2,1), mesh(data), title('"useless" part shown')
subplot(1,2,2), mesh(data.*nan_above_diag_ones_below),
title('"useless" part hidden')