Index in position 1 exceeds array bounds (must not exceed 1).

Hello,

I have the Brownian motion model and I added In the plot a circle with radus R and center (X,Y). However I have two for loops for x and y to calcualte the model and I want to delete some points if they staisfies this condition:

(x(i)-X)^2 +(y(i)-Y)^2<r^2

When I run the code always gave this massage (Index in position 1 exceeds array bounds (must not exceed 1).) Sometimes is change the number such as ( ndex in position 20 exceeds array bounds (must not exceed 29).)

How I let inside the circle empty.

That what I wrote

please anyone help me for my problem with explain how I can solve this problems if I have simoilar in the future.

T=100;
Np=10000;
DX=20;
%Circle --------------------
A=10;
B=10;
R=30; 
th=0:pi/100:2*pi; 
X=R*cos(th)+A; 
Y=R*sin(th)+B; 

%Models
for j=1:m
    for i=1:T 
       x(i+1,j)=x(i,j)+DX*randn();
       y(i+1,j)=y(i,j)+DX*randn(); 
       % Condition--------
       COND= (x(i+1,j)-X).^2+(y(i+1,j)-Y).^2;
       CONDD=int16(trap);
        if trap <r^2     
        x(i+1,j)=[];
        y(i+1,j)=[];
        end 
    end
end

       

[infinity]

Hello,

Several variables are missing in your code, for example m, x, y, trap. Can you show us the code that we can understand welll?

[omar alqubori]

Thank you so much for you try to help me

this is my code:

T=100;
m=10;
A=10;
B=10;
R=30; 
th=0:pi/100:2*pi; 
X=R*cos(th)+A; 
Y=R*sin(th)+B;

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

DX=20;
for j=1:m  %Number of particle
    for i=1:T   %Number of steps
       x(i+1,j)=x(i,j)+DX*randn();
       y(i+1,j)=y(i,j)+DX*randn(); 
       COND= (x(i+1,j)-X).^2+(y(i+1,j)-Y).^2;
       CONDD=int16(COND);

         CONDD<=R^2;
         x(1,:)=[];
         y(1,:)=[];
        

    end    
end


plot(x,y,'k.');
hold on;
plot(X,Y,'r');
title (['Time = ', num2str(T),', Particles = ', num2str(m)]);
xlabel("space x");
ylabel("space y");
hold off;

[infinity]

Hello,

It is clearly that you declare "x = zeros(1,m)" i.e, x is vector having 1 row and m column, but in the loop for, you try to acess x(i+1,j) with i = 1:T. Therefore, if i = 1, then i + 1 = 2 and you will not able to acess the element x(2,j) since x has only 1 row.

[omar alqubori]

Thank you so much for your answer.

However if I cancell the condition the code is working but when I but the condition gave me this massage:

Index in position 1 exceeds array bounds (must not exceed 16).

for different value of m or t

please help me to fix this code

[infinity]

Hello,

What do you mean "cancell the condition"? In your code, there was no condition by using "if" statement. Can you also show your code without errors?

[Walter Roberson]

Suppose you delete entry 5 out of 7. Then afterwards the array would be only 6 long. But you did not adjust the loop bounds, so when you reach the original 7 your index would be out of range. Also if you think about the situation more closely you will see that the entry that was in location 6 and which falls down to occupy location 5, is not having its value examined.

[omar alqubori]

I means by ""cancell the condition"?" If I delete

 COND= (x(i+1,j)-X).^2+(y(i+1,j)-Y).^2;
       CONDD=int16(COND);
         CONDD<=R^2;
         x(i,:)=[];
         y(i,:)=[];

This means that if my code like this

T=100;
m=10;
A=10;
B=10;
R=30; 
th=0:pi/100:2*pi; 
X=R*cos(th)+A; 
Y=R*sin(th)+B;
x = zeros(1,m);
y = zeros(1,m);
DX=20;
for j=1:m  %Number of particle
    for i=1:T   %Number of steps
       x(i+1,j)=x(i,j)+DX*randn();
       y(i+1,j)=y(i,j)+DX*randn(); 
   
    end    
end
plot(x,y,'k.');
hold on;
plot(X,Y,'r');
title (['Time = ', num2str(T),', Particles = ', num2str(m)]);
xlabel("space x");
ylabel("space y");
hold off;

It works but I want appliy this conditin (x(i+1,j)-X)^2-(y(i+1,j)-Y)^2<=R^2 if the condition is satisfies I want delete the points insdie the cyrcle.

Answer 1

[infinity]

Hello,

There are several approaches that you can try to eleminate the point inside the circle. Here, I can show you a solution

T=100;
m=10;
A=10;
B=10;
R=30;
th=0:pi/100:2*pi;
X=R*cos(th)+A;
Y=R*sin(th)+B;
x = zeros(1,m);
y = zeros(1,m);
DX=20;
for j=1:m  %Number of particle
    for i=1:T   %Number of steps
        xnext = x(i,j)+DX*randn();
        ynext = y(i,j)+DX*randn();
        cond =  norm([xnext-A,ynext-B]);
        while (cond < R)
            xnext = x(i,j)+DX*randn();
            ynext = y(i,j)+DX*randn();
            cond =  norm([xnext-A,ynext-B]);    
        end
        x(i+1,j)=xnext;
        y(i+1,j)=ynext;
    end
end
plot(x(2:end,:),y(2:end,:),'k.');
hold on;
plot(X,Y,'r');
title (['Time = ', num2str(T),', Particles = ', num2str(m)]);
xlabel("space x");
ylabel("space y");
hold off;

Now, you will get rid of the previous error.

[omar alqubori]

Dear,

Thank you so much.

You are too smart

Answer 2

[Walter Roberson]

The only way matlab has to delete a single entry out of a multidimensional array is to convert the array to a column vector through linear indexing and do the deletion, leaving a column vector behind. A second index greater than 1 would then be out of range.