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Function definitions are not permitted in this context??

2 次查看（过去 30 天）
Michael
Michael 2013-9-8
I have looked at other posts regarding this subject but nothing they suggested seemed to work for me. I seems that MATLAB doesn't like it when you declare variables prior to the function definition so as you can see in my code that is not the case. I am not sure why it's not working. It seems like it should be pretty simple. I am a mere novice with MATLAB so please go easy on me.
function dydt = Problem4(t,y)
dydt = y*t^3-1.5*y;
[t,y] = ode45(@Problem4, [0, 2], 1);
plot(t,y)
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Michael
Michael 2013-9-8
It should be there now but if not:
function dydt = Problem4(t,y)
dydt = y*t^3-1.5*y;
[t,y] = ode45(@Problem4, [0, 2], 1);
plot(t,y)
Michael
Michael 2013-9-8
编辑：Azzi Abdelmalek 2013-9-8
If I run it directly from the editor window it seems to work however, it is telling me that my "y" argument is undefined. I thought I defined it in the line;
[t,y] = ode45(@Problem4, [0, 2], 1);
I thought the "1" is my "y" value. [0, 2] is the rang of "t" and 1 should "y."
Further help will be very appreciated, thanks in advance!

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回答（3 个）

Image Analyst
Image Analyst 2013-9-8
编辑：Image Analyst 2013-9-8
It seems like Problem4 is trying to call Problem4 inside of itself. Is it your intent to call this recursively? What function do you want to pass in to ode45?
Maybe you want this. I put all of this code below into a single m-file called Problem4.m and it worked:
function Problem4()
[t,y] = ode45(@ConstructEquation, [0, 2], 1);
plot(t,y)
function dydt = ConstructEquation(t,y)
dydt = y*t^3-1.5*y;
Azzi Abdelmalek
Azzi Abdelmalek 2013-9-8
function dydt = Problem4(t,y)
dydt = y*t^3-1.5*y;
% save this function as Problem4.m
In another m file or in Matlab windows command run:
[t,y] = ode45(@Problem4, [0, 2], 1);
plot(t,y)
  2 个评论
Michael
Michael 2013-9-8
That worked. Is it because I have to "call" the function in the command window? I think I get it now...Thanks so much for your help.
Image Analyst
Image Analyst 2013-9-8
No, you don't have to call the function in the command window. It can be all in one single m-file, like I showed.

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Arthur
Arthur 2013-9-8
You cannot define functions in the command window. They have to be in an m-file.

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