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ERROR // Array indices must be positive integers or local values

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Ryan Coder
Ryan Coder le 15 Déc 2022
Commenté : Ryan Coder le 15 Déc 2022
Hello! I have been working on this script for a little bit, and cant seem to figure out why I am getting this error:
" Array indices must be positive integers or logical values.
Error in Q1 (line 33)
set(h,'Color',colorData(rand1)); "
The program is meant to animate a point traveling along a path over over time, changing marker and color randomly with each point. It also reports the runtime of the overall script.
The error changes line every time the script runs between the different set functions. Sometimes it runs fine with no problem. After attempting to debug with disp, I have not seen a value that aligns with the error. Am I missing something?
%%%%%%SCRIPT%%%%%%%
tic
file = fopen('DATA.xlsx');
data = xlsread('DATA','sheet1','A1:B20');
x = data(:,1);
y = data(:,2);
colorData = ["red","green","blue","cyan","magenta","yellow","black","white"];
shapeData = ["o","+","*",".","x","_","|","square","diamond","^","v",">","<","pentagram","hexagram"];
rand1 = 0;
rand2 = 0;
figure(1);
h = plot(0,0);
xlim([0 21]);
ylim([0 6])
for ii = 1:20
rand1 = round(rand*8);
rand2 = round(rand*15);
%x(ii),y(ii),'Color',colorData(rand1),'Marker',shapeData(rand2)
set(h,'Xdata',x(ii));
set(h,'Ydata',y(ii));
disp(rand1)
set(h,'Color',colorData(rand1));
set(h,'Marker',shapeData(rand2));
%I DONT UNDERSTAND WHY IT WORKS SOMETIMES AND NOT OTHERS :(
%drawnow;flushdata;
pause(0.2);
end
t = toc;
fprintf(append('The total program runtime was: ',num2str(t)));

Réponse acceptée

Voss
Voss le 15 Déc 2022
The error happens because sometimes the random value returned from rand is small enough that rand1 or rand2 is 0.
Try replacing this
rand1 = round(rand*8);
rand2 = round(rand*15);
with this:
rand1 = randi(8);
rand2 = randi(15);
  3 commentaires
Ryan Coder
Ryan Coder le 15 Déc 2022
Thanks!!
Voss
Voss le 15 Déc 2022
You're welcome!

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Plus de réponses (2)

Bora Eryilmaz
Bora Eryilmaz le 15 Déc 2022
Modifié(e) : Bora Eryilmaz le 15 Déc 2022
In MATLAB, array indexing is 1-based, not 0-based. The first element of colorData, etc. would be colorData(1). Occasionally, rand command would produce a small enough value such that
rand1 = round(rand*8)
rand1 = 8
would be 0. So, instead of round(), use ceil(), which would guarantee value at or above 1:
rand1 = ceil(rand*8)
rand1 = 6
Better yet, use randi() to produce integer random numbers: https://www.mathworks.com/help/matlab/ref/randi.html

millercommamatt
millercommamatt le 15 Déc 2022
It's because you can round to zero which is invalid as an index. Use ceil instead.

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