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
end
end
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
end
end

Best Answer

  • It's the subtle difference between these two lines of code:
    xAK_val = [xAK-.5, xAK + .5, xAK + .5, xAK -.5];
    yAK_val = [yAK-.5, yAK + .5, yAK + .5, yAK - .5];
    Specifically, the last element of each of these vectors.
    yAK - .5
    is a single element, equal to yAK minus 0.5. But
    xAK -.5
    is two elements, xAK and -0.5.
    (Note that you have that same difference in several places.)