# Using Heun's Method but Problem With Increment

2 ビュー (過去 30 日間)
Hi everyone,
I'm really new to programming and try to use Heun's Method to this skydiving problem, but I kept getting this error, "Unable to perform assignment because the left and right sides have a different number of elements. Error in EulervsHeunStart (line 17)
vh(i) = vh;"
I know I have to use the increment to get the second slope (corrector). Here's my script:
while t<=tend
%save both velocities at time ti
vh(i) = vh;
ve(i) = ve;
tim(i)= t;
%good old Euler
a = g-c/m*ve.^2;
ve = ve+a*dt;
% x = x+v*dt;
%Heun: compute slope at ti
a = g-c/m*vh.^2;
%compute predicted velocity at ti+1
vh = vh+a*dt;
%compute second slope at v(ti+1)
a = g-c/m*vh(i).^2;
vh(i+1) = vh(i)+a*dt;
%compute average of both slopes
%use average slope for extrapolating v from ti to ti+1
%increments
t=t+dt;
i=i+1;
end
Thank you!
##### 2 件のコメント表示非表示 1 件の古いコメント
Hi darova,
please find the attachment for the whole code, but they're pretty much the same as I put on the question and 've' and 'vh' variables are for velocity using euler and velocity using heun respectively. I'd like to compare the error.
Many thanks

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### 回答 (1 件)

darova 2021 年 8 月 29 日
I think you should use index (i) everywhere. vh variable has two elements after first iteration
You trying to assign two elements into one position in this line
vh(i) = vh;
##### 1 件のコメント表示非表示 なし
I've used all index on every ve and vh, but it even said, "Unable to perform assignment because the left and right sides have a different number of elements.
Error in EulervsHeunStart (line 17)
vh(i) = vh;"
I don't understand how this works, but thanks again darova. I really appreciate your help

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