random generation of fractions

Hello, I have fractions such as 1/720,1/360,1/90. How do i randomise them? these numbers are the spatial frequencies which are in cycles/pixel(by default in psychtoolbox). I would like to have a grating with many spatial frequencies generated randomly. Appreciate any help. Thanks Anwesha

Answer 1

[KSSV]

a = 90;
b = 720;
r = (b-a).*rand(100,1) + a;

F = 1./r

[Anwesha]

Thanks, but I want only those specific values that I mentioned. The problem is that spatial frequency is not the same when I run it with 0.001 instead of 1/720. With 'many' I meant 1/720,1/360, 1/180,1/90, 1/45.

[KSSV]

F = [1/720,1/360, 1/180,1/90, 1/45] ;
idx = randperm(length(F),length(F)) ;
Fr = F(idx) ;

[Anwesha]

Technically you are right. But now my code doesnt run at all. Let me know if you want to have a look at my code.

[KSSV]

Off course yes...if you have a problem.

[Anwesha]

function DriftDemo4(angle, cyclespersecond, freq, gratingsize, internalRotation)

AssertOpenGL;

sca;
close all;
clearvars;

PsychDefaultSetup(2);

screens = Screen('Screens');

screenNumber = 0;

white = WhiteIndex(screenNumber);
black = BlackIndex(screenNumber);

blackColor = [0, 0, 0];
whiteColor = [1,1,1];
greyColor = [0.5,0.5,0.5];
spotRect = [1900,1180,1920,1200];

grey = white / 2;

[window, windowRect] = PsychImaging('OpenWindow',screenNumber, grey);

ifi = Screen('GetFlipInterval', window);

topPriorityLevel = MaxPriority(window);
Priority(topPriorityLevel);

numSecs = 2 ;
numFrames = round(numSecs / ifi);

waitframes = 1;

for frame = 1:numFrames
    if KbCheck
        sca;
        return;
    end
    % Color the screen black
    Screen('FillRect', window, blackColor);
    Screen('FillRect', window, whiteColor,spotRect );   % draw white spot

      % Flip to the screen
      Screen('Flip', window);

end

vbl = Screen('Flip', window);

Priority(topPriorityLevel);
vbl = Screen('Flip', window);

for frame = 1:numFrames
    if KbCheck
        sca;
        return;
    end
    % Color the screen grey
    Screen('FillRect', window, greyColor,windowRect );
    Screen('FillRect', window, blackColor,spotRect );   % draw black spot
    % Flip to the screen
    vbl = Screen('Flip', window, vbl + (waitframes - 0.5) * ifi);

end
Priority(0);

Screen('Preference', 'SkipSyncTests', 1);

if nargin < 5 || isempty(internalRotation)
    internalRotation = 0;
end

if internalRotation
    rotateMode = kPsychUseTextureMatrixForRotation;
else
    rotateMode = [];
end

if nargin < 4 || isempty(gratingsize)
    gratingsize = 720;
end

res = [1920 1200];

if nargin < 3 || isempty(freq)
    % Frequency of the grating in cycles per pixel: Here 0.01 cycles per pixel:
    %    freq = 1/720;
    %    freq= [1/360;1/720;1/180;1/90];

      F = [1/720,1/360, 1/180,1/90, 1/45] ;
      idx = randperm(length(F),length(F)) ;
      Fr = F(idx) ;

      %      freq = 1/180;
  end

if nargin < 2 || isempty(cyclespersecond)
    cyclespersecond = 0.17;
end

if nargin < 1 || isempty(angle)
    % Tilt angle of the grating:
    angle = 0;
end

amplitude = 0.5;
phase = 0;

phaseincrement = (cyclespersecond * 720) * ifi;

gratingtex = CreateProceduralSineGrating(window, res(1), res(2), [0.5 0.5 0.5 0.0]);

KbReleaseWait;

while ~KbCheck

      phase = phase + phaseincrement;

      msize = numel(Fr);
      for a = 1:msize
      freq1= freq(randperm(msize,1));

      Screen('DrawTexture', window, gratingtex, [], [], angle, [], [], [], [], rotateMode, [phase, freq1, amplitude, 0]);
      Screen('FillRect', window,  [1,1,1],spotRect);
      vbl = Screen('Flip', window, vbl + 0.5 * ifi);

      end
      %
  end
  % We're done. Close the window. This will also release all other ressources:
  sca;

end

[Anwesha]

KSSV...could you figure out what the problem is?

[KSSV]

Can you give me a input which you have tried? I mean how did you call the function?

[Anwesha]

I made changes on the demo code and ran it. Thats how i have done with multiple orientations. freq was the input

[Anwesha]

if nargin < 3 isempty(freq) % Frequency of the grating in cycles per pixel: Here 0.01 cycles per pixel: % freq = 1/720; % freq= [1/360;1/720;1/180;1/90];

    freq = [1/720,1/360, 1/180,1/90, 1/45] ;
    idx = randperm(length(freq),length(F)) ;
    Fr = freq(idx) ;

    %      freq = 1/180;
end

[Anwesha]

msize = numel(Fr); for a = 1:msize freq1= Fr(randperm(msize,1));

    Screen('DrawTextu re', window, gratingtex, [], [], angle, [], [], [], [], rotateMode, [phase, freq1, amplitude, 0]);
    Screen('FillRect', window,  [1,1,1],spotRect);
    vbl = Screen('Flip', window, vbl + 0.5 * ifi);

    end

[Anwesha]

This is the part of the code where I made the changes..not able to figure out what is going wrong