Error:undefined variable in trapezoidal integration

3 次查看（过去 30 天）
Yo mama
Yo mama 2020-4-28
评论： Rena Berman 2020-5-14
Ok this is driving me crazy because it seems so simple. All i need to do is integrate from t=0 and t=3. I have the following function and the comments are what I put into the command window. I need to integrate the ydot vector but once I put it in the function is says that ydot is not defined like what.
  2 个评论
Stephen23
Stephen23 2020-4-30
Original question by Yo mama retrieved from Google Cache:
"Error:undefined variable in trapezoidal integration"
Ok this is driving me crazy because it seems so simple. All i need to do is integrate from t=0 and t=3. I have the following function and the comments are what I put into the command window. I need to integrate the ydot vector but once I put it in the function is says that ydot is not defined like what.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Brian Iwatake
Brian Iwatake 2020-4-28
If you "clear all", then ydot is not there anymore, right?
  6 个评论
显示 4更早的评论
Brian Iwatake
Brian Iwatake 2020-4-30
Hi, I'm still missing something. I didn't have your "ydot", so for my "ydot", I created a simple arbitrary ramp function, ydot = (0 : 2/3 : 100), which is just some big vector - I didn't want to run out of data points.
I = trapezoidal(f, 0, 3, 0.1) was your original function call.
try doubling the step size:
I = trapezoidal(f, 0, 3, 0.2)
For my "ydot" ramp function, the integration result is exactly half. This is not correct.
For your "ydot" data, do you get a reasonable answer for both trapezoidal(f, 0, 3, 0.1) and trapezoidal(f, 0, 3, 0.2)?
Does your result make sense to you?
As you make the step size "h" smaller, your integration result converges to the exact answer. For example, the integration result (usually) shouldn't double every time you cut "h" in half.
Yo mama
Yo mama 2020-4-30
  1. my step size was fixed for the question being asked, the result of my integration was compared to my runge-kutta result for the distance at 3 seconds and I got a percent error of less than one percent - so I think it was spot on, my code only worked when I ran a Sys2ODEsRK4 function as well in another window. My step size needed to be 0.1 explicitely.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Linear Algebra 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by