Keep getting "Index exceeds number of array elements (1)" message

Hi, I have this code below, which works when I simplify the code to simply add to either x or y arrays, but doesn't work when I'm doing both, can anyone help me figure out why this may be? I'm being told from the error message that there's something wrong with "x(t)=x(t-1)-1;"

x(1)=0;
y(1)=0;

c=clock;
z=c(1,6)*1000;
rand('seed',z);

for i=1:50
    r(i)=floor((3-1)*rand(1)+1);
    r2(i)=floor((5-1)*rand(1)+1);
end

for t=2:50
    if r(t)==1
        if mod(r2(t),2)==0
            x(t)=x(t-1)+1;
        else
            x(t)=x(t-1)-1;
        end
    end
    if r(t)==2
        if mod(r2(t),2)==0
            y(t)=y(t-1)+1;
        else
            y(t)=y(t-1)-1;
        end
    end
end

disp(x)
disp(y)

[Toey]

Hi Reem,

In your code, x & y only increase their sizes when r(t)==1 and r(t)==2, but your index t increases by 1 every loop. This is when there's mismatch between indexing and the size of x,y.

To fix the issue, you can preallocate x,y in the beginning of your code

x=zeros(50,1); y=zeros(50,1);

or having x(t) =0 in the else statement when r(t)==1 isn't met.

[Reem Gawish]

Just tried this and got it working! Thanks so much!

Answer 1

[Sriram Tadavarty]

Hi Reem,

Make minor modification to the code to avoid that error as shown below:

x(1)=0;
y(1)=0;

c=clock;
z=c(1,6)*1000;
rand('seed',z);

for i=1:50
    r(i)=floor((3-1)*rand(1)+1);
    r2(i)=floor((5-1)*rand(1)+1);
end

for t=2:50
    if r(t)==1
        if mod(r2(t),2)==0
            x(t)=x(t-1)+1;
        else
            x(t)=x(t-1)-1;
        end
    else
        x(t) = 0; % Added this to ensure that value is stored as zero, when r(t) is not equal to 1
    end
    if r(t)==2
        if mod(r2(t),2)==0
            y(t)=y(t-1)+1;
        else
            y(t)=y(t-1)-1;
        end
    else
        y(t)=0; % Added this to ensure that value is stored as zero, when r(t) is not equal to 2
    end
end

disp(x)
disp(y)

Hope this helps.

Regards,

Sriram

[Reem Gawish]

Thanks so much for your help! Finally understood what the problem was lol