Error:undefined variable in trapezoidal integration

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Yo mama 2020-4-28

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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.

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Stephen23 2020-4-30

Original question by Yo mama retrieved from Google Cache:

"Error:undefined variable in trapezoidal integration"

Rena Berman 2020-5-14

(Answers Dev) Restored edit

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回答（1 个）

Brian Iwatake 2020-4-28

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If you "clear all", then ydot is not there anymore, right?

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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 2020-4-30

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.

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