请帮助：在分配A（I）= B中，B和I中的元素数必须相同。 的MATLAB

Question

I was asked in an assignment to use Euler's method to determine the values of t and y from t=0:1000. I have all the basic code and parameters down but when i put my Euler's equation in I get the error code

In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in Project1 (line 24) Ay(i+1) = Ay(i) + (dAy)*x;

How could I change these variables between vectors and scalars to allow the equation to run? My full code can be found below:

dt=x;
Ay=zeros(1,1001);
Ay0=1250;
Ay(1) = Ay0;
t=0;
y=0;
t=0:dt:1000;
for i=1:1000
    if y > 10
        Qout=3*(y-10).^1.5;
    else
        Qout=0;
    end
    Qin=1350*sin(t).^2;
    dAy=Qin-Qout;
    Ay(i+1) = Ay(i) + dAy*dt;
end
plot(t,y);

Answer 1

The problem lies in the line of your code:

Ay(i+1) = Ay(i) + dAy*dt;

dAy*dt returns a vector.

When you add it to Ay(i) you still end up with a vector.

Ay(i+1) is a SINGLE element within a vector.

You Cannot assign a vector quantity to an element within a vector.

Answer 2

The issue is that your variable "Qin" is not a number it is a vector containing sin values of the whole vector t. Similarly your "dAy" is also a vector. Hence it cannot be stored in a variable Ay.
if your dt =x = 1, just replace sin(t) with sin(i) ie replace

Qin=1350*sin(t).^2; by Qin=1350*sin(i).^2;