Array indices must be positive integers or logicsal values

I've been trying to code a min and max calculator for a function named Ey. However, it says that my array indices must be positive integers or logical values. I've kept trying new things but cannot get anything to work. Can anyone solve this for me? Thanks, probably something stupid, very new to matlab.

clear; clc;
%input data
r=0.35; %length of crank OA in m
a=0.65; %length of the distnace BA in m
b=0.5; %length of the distnace AC in m
m=0.8; %ength of the link CD in m
d=1.3; %distance(m) of vertical axis of third slider from O
t=0.75; %length of the length DE
w=1.5; %angular velocity of crank in rad/s

%===============computaion===================
%p=alpha
%q=theta
    
k=0;
for q=0:1:6283
    k=k+1;
    p=asin((7*sin(q))/13);
    v(k)=(a+b)*sin(p);
end



p=asin((7*sin(q))/13);
v=(a+b)*sin(p);
DF=sqrt((m^2)-(v.^2));
OF=(a+b)*cos(p)-(13*sin(pi-q-p)/20.*sin(q));
OD=OF+DF;
Ey=sqrt(t^2-(d-OD).^2);

%NOTE ===== try and divide 2pi by 1000, then change step to 1, then just
%divide at the end.


k=0; step=1;
for q=0:step:6283
    k=k+1;
    x(k)=q;
    y(k)=Ey(q);
end



min=y(1);indx1=1;
for i=2:k
    if y(i)<min;
        min=y(i);
        indx1=i;
    end
end

max=y(1); indx2=1;
for i=2:k
    if y(i)>max;
        max=y(i);
        indx2=i;
    end
end

    


disp('Min of Ey = ');
disp(min);
disp('obtained at q = ');
disp(q_min);
plot(x,y);




for q=0:step:2*pi
    k=k+1;
    y(k)=Ey(q);
    x(k)=q;
if(Ey(k)<min)
    min=Ey(k);
    q_min=q(k);
end
end

Answer 1

[Matt J]

The intention of this part of the code is unclear

k=0; step=1;
for q=0:step:6283
    k=k+1;
    x(k)=q;
    y(k)=Ey(q);
end

Aside from q=0 being an invalid index, Ey is a scalar, so indexing at q>1 would also be invalid.

K>> Ey

Ey =

    0.4466