redefine array in for loop

Hi Guys,

   for n = 3:length(x)
      y1 = x(2:n) ;
      t1 = ((n-2):-1:0)*dt ;
     % y2 = x(1:n-1) ;
      y2 = y1 - 1 ;
      t2 = t1 +dt; 
      int(n) = sum (t1.^(k-1)/factorial(k-1).*y1 + t2.^(k-1)/factorial(k-1).*y2)*dt/2 ;

end

I want to define y2= y1 -1 instead y2= x (1:n-1) which I have commented above. By y2 = y1 - 1, occurred some errors in MATLAB. Why? It is not correct?

What error did you encounter with the code you tried?

Answer 1

y1-1 means the vector y1 with the quantity 1 subtracted from it. The commented code shifts the elements by one element. Which do you want to do?

I intend instead of defining the variable y2 with x(1:n-1) , define it by y1 -1 . Maybe I can omit the y2 variable.

could you give us an exemple of x ??? I'm ok with John y2 = x(1:n-1) and y2 = y1 - 1 , it's not the same thing !!!

I think you want to shift the elements by 1, but you want to define it your own way. If you want to use Matlab, you need to use it's syntax.

int = zeros(1,length(x));
if k <= 0
    int = x ;
    return
end

for n = 3:length(x)

      y1 = x(2:n) ;

      t1 = ((n-2):-1:0)*dt ;
     y2 = x(1:n-1) ;

     % y2 = -1 +y1 ;
      t2 = t1 +dt; 
      int(n) = sum (t1.^(k-1)/factorial(k-1).*y1 + t2.^(k-1)/factorial(k-1).*y2)*dt/2 ;

end

I mean, is there anyway to define y2 from y1? And not from variable x? Could I omit the variable y2 from the code ?

If you don't use y1 and y2 after...

   if k <= 0
     int = x ;
     return
   else
     int = zeros(1,numel(x));
   end

   for n = 3:numel(x)
      t1 = ((n-2):-1:0)*dt ;
      t2 = t1 +dt; 
      int(n) = sum ( ...
         t1.^(k-1)/factorial(k-1) .* x( 2 : n   ) + ...
         t2.^(k-1)/factorial(k-1) .* x( 1 : n-1 ) ...
         )*dt/2 ;
   end