How to set a point to change color in colorbar

I want to use scatter3 with particles and want to have different color for positive and negative values of charge or velocities. I use this code through a Simulink prototype " Spiral Galaxy Formation Simulation "

   oldPlot = scatter3(points_x,points_y,points_z,psize,points_col,'filled')

   cmap = [1 0 0 ; 0 1 0 ] ; %2 color bar
   colorbar;
   colormap(cmap)

but when positive or negative gets higher values, then 0 is not the point that the color changes, but it moves towards the middle of the min and max value.

I want all positive to be green and all negative to be red.

I tried this code

   cm=colormap;
   cm(0,:)= [1 0 0];
   colorbar;
   colormap(cm)

but it doesn't seem to work.

[Rik]

Does it need to be one single scatter object? Otherwise you can simply plot the negative part separately from the positive part.

[Christos Dimopoulos]

I am not sure. I have tried that too, but it doesn't suit the project as you can see from the code...

    for i = 1:n,
    points_x(i) = bodies(i,2);
    points_y(i) = bodies(i,3);
    points_z(i) = bodies(i,4);

    MassRange=(log10(abs(bodies(i,1)))-41.0)*500; % /SolarMass;   
    psize(i)=MassRange; % bodies(i,1)/(10e7*SolarMass);
    points_col(i) = bodies(i,1)/SolarMass ; %  MassRange
end

% Remove the old plot.
if isempty(oldPlot)
  oldPlot = fig;
elseif ~isempty(foundFig)

cla
%    delete(oldPlot);
end

 oldPlot = scatter3(points_x,points_y,points_z,psize,points_col,'filled')

I think I need one plot because I compare particles, sizes, I have to make them interact between each other.

Answer 1

[Image Analyst]

Try this:

% Initialization/clean up
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format short g;
format compact;
fontSize = 13;

numPoints = 100;
points_x = rand(1,numPoints) - 0.5;
points_y = rand(1,numPoints) - 0.5;
points_z = rand(1,numPoints) - 0.5;
psize = 40;

% User wants "all positive to be green and all negative to be red."
% First default to all black;
points_col = zeros(numPoints, 3);
% Now find where ALL 3 coords are positive;
allPosIndexes = points_x > 0 & points_y > 0 & points_z > 0;
% Set those to green.
points_col(allPosIndexes, 2) = 1;
% Now find where ALL 3 coords are negative;
allNegIndexes = points_x < 0 & points_y < 0 & points_z < 0;
% Set those to red.
points_col(allNegIndexes, 1) = 1;
% Now one octant will be red, one octant will be green
% and 6 octants will be black.

% Now plot.
oldPlot = scatter3(points_x,points_y,points_z,psize,points_col,'filled')
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
zlabel('Z', 'FontSize', fontSize);

[Image Analyst]

Regarding your so-called "Answer" (which doesn't work)...

Sure, Christos, I'll try to help if you let me. I'll try it if you give me "bodies" in an attached .mat file. Otherwise I can't run your function at all.

[Christos Dimopoulos]

I am truly sorry for that. I am new in Matlab and in this Q&A process. I am not exactly sure how to send you just the bodies function. There is everything in " Spiral Galaxy Formation Simulation " in Mathworks. I have not made any significant changes.

bodies(i,1) is mass, 2-4 3D position, 5-7 3D velocity, and 8 (supposed to be) color (but never worked).

If you need exactly my "Constract Galaxy 1" function just let me know how to sent it as you asked.

I will try to give you the code here, hoping that will help.

       for i = 1:n,
        m0 = rand*20+4;
        m = -10e8*m0*SolarMass;
        r = radiusOuter*(1.1-rand^2); 
        theta = rand*(2*pi);
        phi = acos(1-rand*2); 
        y = r*sin(phi)*cos(theta); %r*2*(0.5-rand);
        z = r*sin(phi)*sin(theta); %r*2*(0.5-rand);
        x = r*cos(phi); % r*2*(0.5-rand); %(rand-1/2)*(radiusOuter - radiusInner)/100;
        dx = 0 ;
        dz = 0 ;
        dy = 0 ;
        % Compute free fall velocity
        v = sqrt(G*cm/r);
        bodies(i,1) = m;
        bodies(i,2) = x+pos(1)*Parsec;
        bodies(i,3) = y+pos(2)*Parsec;
        bodies(i,4) = z+pos(3)*Parsec;
        bodies(i,5) = dx*v+vel(1);
        bodies(i,6) = dy*v+vel(2);
        bodies(i,7) = dz*v+vel(3);
        bodies(i,8) = 'r';
    end

I want you to know that I appreciate your interest in helping me.

[Christos Dimopoulos]

If I understood correctly, what I wrote was not helpful to you. I am attaching the whole program, so you will find functions and connections between them. I hope this helps.

[Image Analyst]

I've added Simulink to the Product list on the right hand side, so that others don't have to waste their time if they don't (like me) have Simulink. I'd say a minority of people here even have Simulink, so when people have a Simulink program, or any program that requires function available only in a certain toolbox or product they list that in the Products section. You might also attach the .mdl file to your original question up top.

Answer 2

[Christos Dimopoulos]

Thank you. I tried to "embed" your code in mine, but it doesn't seem to work. Can you see what's wrong please?

   function PlotAll(bodies)

   persistent fig;
   persistent oldPlot;

   coder.extrinsic('findobj','get','set','figure','clf','hold','text',...
    'addfram','im2frame','delete','plot3','scatter3','psize',...
    'colorbar','drawnow','getframe', 'VideoWriter', 'writeVideo',...
    'open', 'M','num2str', 'cm');

   n = size(bodies,1);

   SpeedOfLight = 299792458; % in m/s
   YearInSeconds = 365*24*60*60;
   ShowStep = 20;
   LightYear = SpeedOfLight*YearInSeconds;
   Parsec = 3.26*LightYear;
   SolarMass = 1.9891e+30;

   foundFig = findobj('Tag','galaxyScreen');

   if isempty(fig)||isempty(foundFig)
    if isempty(foundFig)
        fig = figure;
    else
        fig = figure(foundFig);
    end;
    clf(fig);
    set(fig, 'Name', 'Simulation');
   end

   points_x = zeros(1,n);
   points_y = zeros(1,n);
   points_z = zeros(1,n);
   points_mass = zeros(1,n);
   psize = zeros(1,n);

   % User wants "all positive to be green and all negative to be red."
   % First default to all black;
   points_col = zeros(n, 3);

   for i = 1:n,
    points_x(i) = bodies(i,2);
    points_y(i) = bodies(i,3);
    points_z(i) = bodies(i,4);
    points_mass(i) = bodies(i,1);

    MassRange=(log10(abs(bodies(i,1)))-41.0)*200; % /SolarMass; 
    if MassRange<=4,
        MassRange=4;
    end    
    psize(i)=MassRange; % bodies(i,1)/(10e7*SolarMass);

   end

   % Now find where ALL 3 coords are positive;
   allPosIndexes = points_mass > 0 ;
   % Set those to green.
   points_col(allPosIndexes, 2) = 1;
   % Now find where ALL 3 coords are negative;
   allNegIndexes = points_mass < 0;
   % Set those to red.
   points_col(allNegIndexes, 1) = 1;  

   % Remove the old plot.
   %
   if isempty(oldPlot)
    oldPlot = fig;
     ShowStep=ShowStep+1;
   elseif ~isempty(foundFig)

   cla
   ShowStep=ShowStep+1;
   %    delete(oldPlot);
   end

   oldPlot = scatter3(points_x,points_y,points_z,psize,points_col,'filled')

   %colormap([repmat([0 1 0],-10e10,0); repmat([1 1 0],-10e10,0)]);
   %cm=colormap;
   %cm(0,:)= [1 1 1];
   %cmap = [1 0 0 ; 0 1 0 ] ; %3 color bar
   colorbar('color','w');
   drawnow

It gives me error message...

Logical indexing requires support of variable-sized arrays, which is currently disabled.

Function 'Plot all bodies' (#521.2202.2215), line 89, column 12: "allPosIndexes"

And the same for "allNegIndexes"

_____

Isn't there any easy way to just put the limit to 0 for the 2 colors?

I think the new proposal is way too complicated.

But if we can make it work, it is worth the effort.