I have to plot a linear function and color it in a way that all negative values are red and the positive values are blue.
This is just an example of what I want to ask.
Generalizing, is it possible to color specific intervals of a function in a different color than that of the rest of the function, without having to do different plots?
No. Create a red coloured plot for the negative values, use hold on and then a blue coloured plot for the positive values.
x = [-10:0.1:10].'; %//range
x1 = x(x<=0); %//negative values and zero
x2 = x(x>=0); %//positive values and zero
figure; %//open figure
hold on %// plot things in the same figure
plot(x1,x1,'r') %//plot negative values
plot(x2,x2,'b') %//plot positive values
Related
I am trying to figure out how to use colorbar to show the magnitude rather than the value. Currently colorbar has a range from [-x x] where any negative values are color blue-ish. I want the colorbar to ignore the sign values when determining what color to paint the graph.
I tried setting the range to [0 x] in CLim but that just paints anything that is negative blue.
An example would be plotting a sphere. If you plot a sphere, it would be centered
at the origin and the color would only reflect the value of the z-axis. However, I want the colorbar to show the magnitude of the distance from the center. So, in this case, the sphere should be a solid color representing the radius.
Any ideas?
You must take the magnitude of the data you are plotting (e.g. using the abs(data) function) prior to making a figure with it. Then, you can set the colorbar scale using the caxis([min max]) function.
Example:
rawData=repmat([-10:1:10],10,1);
figure(1),imagesc(rawData),caxis([0 10]) % All raw values below 0 are plotted as blue
magnData=abs(rawData) % Take absolute value of raw data
figure(2),imagesc(magnData),caxis([0 10]) % Raw negative values are now plotted in the same color as positive raw values (i.e. ignoring the sign, per the solution you requested).
Your solution (CLim) didn't work because setting the color range [0 x] will associate color of all values lower than 0 to the value of 0 (blue, in the case of the "jet" colormap).
I am trying to make a simple plot (for this example doing a plot of y=x^2 will suffice) where I want to set the colors of the points based on their magnitude given some colormap.
Following along my simple example say I had:
x = 1:10;
y = x.^2;
Use gscatter(x,y,jet(10)); legend hide; colorbar which produces a plot with the points colored but the colorbar does not agree with the colored values. (Can't post picture as this is my first post). Using a caxis([1,100]) command gives the right range but the colors are still off.
So I have two questions:
(1) How can I fix the colors to fit to a colorbar given a range? In my real data, I am looking at values that range from -50 to 50 in some instances and have many more data points.
(2) I want to create a different plot with the same points (but on different axes) and I want the colors of each point on this new plot to have the same colors as their counterparts in the previous plot. How can I, programmatically, extract the color from each point so I can plot it on two different sets of axes?
I would just move the points into a matrix and do an imagesc() command but they aren't spaced as integers or equally so simple scaling wouldn't work either.
Thanks for any help!
Regarding you first question, you need to interpolate the y values into a linear index to the colormap. Something like:
x = 1:10;
y = x.^4;
csize = 128;
cmap = jet(csize);
ind = interp1(linspace(min(y),max(y),csize),1:csize,y,'nearest');
scatter(x,y,14,cmap(ind,:),'filled')
colorbar
caxis([min(y) max(y)])
Using interp1 in this case is an overkill; you could calculate it directly. However, I think in this way it is clearer.
I think it also answers your 2nd question, since you have the index of the color of each data point, so you can use it again in the same way.
I have 2d line plot in matlab where each line is colored according to a value. I would like to add a colorbar showing the color that corresponds to these values.
I got a solution to plot the lines according to the value I want, however I can not figure out to get the colorbar correctly. I have been searching on this but I am stuck.
Define an RGB color matrix COL.
(N x 3 low red to dark matrix corresponding to equally spaced values 0:1).
Sort the data according to their z value.
Interpolate the COL matrix to get values for all z values, giving the TRUECOL matrix for the lines.
Set the axiscolor-ordering to the TRUECOL matrix and plot the data.
minimalistic example:
% Generate 10 lines of 10 points
x = normrnd(0,1,10,10);
% The corresponding values are
% Note that these do not have to linearly spaced in real code
z = [0,0.05,0.1,0.11,0.12,0.2,0.4,0.45,0.8,0.9];
% Define colormatrix
COL = [0.996078431372549 0.878431372549020 0.823529411764706;...
0.937254901960784 0.231372549019608 0.172549019607843;...
0.403921568627451 0 0.0509803921568627];
% Interpolate the COL matrix to get colors for the data
TRUECOL = interp1(linspace(0,1,3),COL,z,'pchip');
% Set the axis coloring qnd plot the data
set(gcf,'DefaultAxesColorOrder',TRUECOL);
plot(x);
colormap(TRUECOL);
colorbar
I then change the colormap and plot the colobar, however the colors in the colorbar to not correspond to the values z. Is there a way of telling matlab which color corresponds to which value? Looking at the colorbar editor I see that CData must have something to do with it, but I cant find a way to specify that CData should be z.
My understanding is that you want the labels on the colorbar to go from 0 to 1, not 0 to 11. To fix this, use this caxis command. To get finer gradations of colors in the colorbar, you need to more finely interpolate the colormap. Try this:
colormap(interp1(linspace(0,1,size(COL,1)), COL, linspace(0,1,100)));
caxis([0,1]);
colorbar
I would like to plot a sort of "density map" in Matlab, but have not found the right tool yet.
I have "continuous" data with x between (x_min and x_max), and y between (y_min and y_max). At each of these pairs of points (x_i,y_i), there is associated to it a value between 0 and 1.
I would like to plot this information in a 2d graph, such that in each small square containing (x_i,y_i) the plot shades the square black for the value 0, white for the value 1, and the appropriate shade of gray for intermediate values.
Can this be done easily in Matlab?
http://www.mathworks.com/help/images/ref/mat2gray.html seems to do exactly what I need.
If the data is in a matrix A, you can just use
image(255*A); colormap gray(256); axis image;
I'm not sure what you mean by continuous (uniformly spaced?), so my answer won't make too many assumptions other than that there is a reason why you mention the coordinates (if just a regular mesh, then just image or imagesc). So, only assuming your x and y coordinates are possibly non-uniformly spaced, but at least monotonically increasing samples, try surf with view(2):
surf(X,Y,data)
view(2)
colormap gray
By default surf sets the FaceColor property with the 'flat' option:
flat — The values of CData determine the color for each face of the surface. The color data at the first vertex determine the color of the entire face.
In other words, the value will determine the shade.
Assuming your data is in data and your x and y coordinates are in x and y, here is how to do it:
imagesc(x, y, data) % to create a heat map
colormap(gray) % for gray levels
caxis([0 1]) % to set 0 to black and 1 to white
axis xy % if you want the y axis to point up
colorbar % to display the colorbar
In a 3D scatter graph of MATLAB I have 15 different clusters of data that I want to highlight. I can see MATLAB has 8 specific colors. Is there any other way I could use 7 more colors just to distinguish the clusters?
Thanks
I would recommend to use this File Exchange submission - Generate maximally perceptually-distinct colors
It allows you to create a colormap with very distinguished colors and apply them with COLORMAP function. See help for this submission for more options.
colors = distinguishable_colors(n_colors);
For 3D scatter you can use this colors as an argument (C) in SCATTER3:
scatter3(X,Y,Z,[],colors)
To use this colors for different lines set them as default color order either for current figure:
set(gcf,'DefaultAxesColorOrder',colors)
or all figures:
set(0,'DefaultAxesColorOrder',colors
You can use the color property using set. You must first get a handle h to the drawing objects and set(h,'color',[0.2 0.3 0.9]). The color is rgb ranging from 0 to 1 for each channel.
From the Matlab documentation:
scatter(X,Y,S,C) displays colored circles at the locations specified
by the vectors X and Y (which must be the same size).
S determines the area of each marker (specified in points^2). S can be
a vector the same length as X and Y or a scalar. If S is a scalar,
MATLAB draws all the markers the same size. If S is empty, the default
size is used.
C determines the color of each marker. When C is a vector the same
length as X and Y, the values in C are linearly mapped to the colors
in the current colormap. When C is a 1-by-3 matrix, it specifies the
colors of the markers as RGB values. If you have 3 points in the
scatter plot and wish to have the colors be indices into the colormap,
C should be a 3-by-1 matrix. C can also be a color string (see
ColorSpec for a list of color string specifiers).
So, for example, say that your clusters are given by the columns of the matrices X and Y, with the k'th column being the k'th cluster, X being the X coordinates, and Y being the Y coordinates. We can do what you want as follows:
% make some random data in clusters:
n = 15;
m = 42;
X = 0.2*rand(m,n) + repmat(rand(1,n),m,1);
Y = 0.2*rand(m,n) + repmat(rand(1,n),m,1);
% lets change the colour map:
colormap(jet);
% now plot each, one at a time, and each with a different colour:
hold on;
for k=1:n
scatter(X(:,k),Y(:,k),40,k/n*ones(m,1));
end
If you don't like these colours, you can change the colormap, and if you don't like the color maps, you can, as the other answer points out, insert any RGB values you want.