# MATLAB: Running code and getting error about vector must be the same length

vector

I'm running my code and I am getting an error about how the vector must be the same length. Does anyone have advice because I thought the vectors were fillled to the same length?
``ntrails = 20;N_run = zeros(ntrails,1);BC = [5,-5,-5,5];for trail = 1:1:ntrails    xA = -5; xAK = xA;    yA= 0; yAK = yA;    xB = 5; xBK = xB;    yB = 0; yBK = yB;    nsteps = 1000;    collision_flag = 0; k = 0; while collision_flag == 0 && k < nsteps     [xAKp1, yAKP1] = RandWalk_2D(xAK,yAK,BC);     [xBKp1, yBKP1] = RandWalk_2D(xBK,yBK,BC);          xAK_val = [xAK-.5, xAK + .5, xAK + .5, xAK -.5];     yAK_val = [yAK-.5, yAK + .5, yAK + .5, yAK - .5];          xAKp1_val = [xAKp1-.5, xAKp1 + .5, xAKp1 + .5, xAKp1 -.5];     yAKp1_val = [yAKp1-.5, yAKp1 + .5, yAKp1 + .5, yAKp1 - .5];               xBK_val = [xBK-.5, xBK + .5, xBK + .5, xBK -.5];     yBK_val = [yBK-.5, yBK + .5, yBK + .5, yBK - .5];          xBKp1_val = [xBKp1-.5, xBKp1 + .5, xBKp1 + .5, xBKp1 -.5];     yBKp1_val = [yBKp1-.5, yBKp1 + .5, yBKp1 + .5, yBKp1 - .5];          figure(1)     hold on     xlim([-5.5,5.5,])     ylim([-5.5,5.5,])     fill(xAK_val,yAK_val,'r') %current step A     fill(xAKp1_val, yAKp1_val, 'b')%next step for A     fill(xBK_val,yBK_val,'r') %current step B     fill(xBKp1_val, yBKp1_val, 'b')%next step for B     hold off          xAK = xAKp1; yAK = yAKp1;      xBK = xBKP1; yBK = yBKp1;     k = k+1;         if xAK == xBK && yAK == yBK        collision_flag = 1;        N_run(trail) = k;    end endend medval = median(N_run)    function [x,y] = RandWalk_2D(x0,y0,BC)   r = rand;   if r<0.2        x = x0;        y = y0+1;        if y >= BC(1); y = BC(1);        end   else if 0.2 < r && r <= 0.4;           x = x0;           y = y0-1;           if y <= BC(2);               y = BC(2);           end       elseif 0.4< r && r<=0.6           x = x0 - 1;           y = y0;           if x<= BC(3); x = BC(3)           end       elseif 0.6 < r && r <= 0.8;           x = x0+1; y = y0;           if x >= BC(4); x = BC(4);           end       elseif 0.8<r            x = x0; y = y0;       end   endend``

``xAK_val = [xAK-.5, xAK + .5, xAK + .5, xAK -.5];yAK_val = [yAK-.5, yAK + .5, yAK + .5, yAK - .5];``
``yAK - .5``
``xAK -.5``