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

I am solving rungekutta equation of order K_4. However I am getting the above error at the final part when I want to conclude the main equation. See the code;

dm =  @(t_1,r)Tau.*M_T'.*Free_area'.*v./(D_p.*t_1); 

for i=1:(length(x)-1)                              % calculation loop
    k_1 = dm(x(i),y(i));
    k_2 = dm(x(i)+0.5*h,y(i)+0.5*h*k_1);
    k_3 = dm((x(i)+0.5*h),(y(i)+0.5*h*k_2));
    k_4 = dm((x(i)+h),(y(i)+k_3*h));

      y(i+1) = (1/6)*(k_1+2*k_2+2*k_3+k_4)*h;        % main equation

end

I can get only one vector of the right side of the equation but I need an array . I know my problem is to do with the left side of the main equation as I didn't locate enough space for the output array but how can I do it? any help?

Answer 1

[Walter Roberson]

Perhaps

y(:,i+1) = (1/6)*(k_1+2*k_2+2*k_3+k_4)*h;

instead of the assignment you have.

[Nicholas]

yes. It worked. thanks