Please help with using ode45

Question

Christopher Carey 2018-4-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/397424-please-help-with-using-ode45

评论： Walter Roberson 2018-4-26

Please assist me with resolving the errors I'm getting.

Heres my functions:

function output=funct(A,B,C,D,E,F,tmin,tmax)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);
plot(t,y(:,1))
end

This is the function im attempting to cal

function ydot=func(t,y)
ydot(1)=y(2);
ydot(2)=y(3);
ydot(3)=((F*exp(-0.1*t)*cos(t))+(B*y(3))-(C*t*y(2))+(E*y(1)))/A;
ydot=ydot';
end

Here are my erros

Cannot find an exact (case-sensitive) match for 'F'
The closest match is: f in C:\Users\Christopher\Documents\MATLAB\f.m
Error in func (line 4)
ydot(3)=((F*exp(-0.1*t)*cos(t))+(B*y(3))-(C*t*y(2))+(E*y(1)))/A;
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
Error in ode45 (line 115)
      odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in funct (line 2)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);

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Star Strider 2018-4-26

Related: ode45 for third order differential (link)

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Answer 1

Walter Roberson 2018-4-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/397424-please-help-with-using-ode45#answer_317237

You need to pass some of the variables into your fun.

http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

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Christopher Carey 2018-4-26

编辑：Walter Roberson 2018-4-26

在 MATLAB Online 中打开

Hey trying to attempt this but still getting errors

New Code:

function output=funct(A,B,C,D,E,F,tmin,tmax)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);
function ydot=func(t,y)
ydot(1)=y(2);
ydot(2)=y(3);
ydot(3)=((F*exp(-0.1*t)*cos(t))+(B*y(3))-(C*t*y(2))+(E*y(1)))/A;
ydot=ydot';
end
plot(t,y(:,1))
end

Error:

>> func(1, 5, 7, 9, 11, 13, 0, 20)
Not enough input arguments.
Error in func (line 2)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
Error in ode45 (line 115)
    odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in func (line 2)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);

Walter Roberson 2018-4-26

在 MATLAB Online 中打开

You need to change

[t,y]=ode45('func',[tmin tmax],[0 0 0]);

to

[t,y] = ode45(@func,[tmin tmax],[0 0 0]);

You posted,

>> func(1, 5, 7, 9, 11, 13, 0, 20)
Not enough input arguments.
Error in func (line 2)
[t,y]=ode45('func',[tmin tmax],[0 0 0]);

However, that code does not occur on line 2 of func. Line 2 of func is the empty line between the 'function' header and the line

ydot(1)=y(2);

That code instead appears at line 2 of funct . With your having defined func as a nested function, there is no way you could have called func directly from the command line.

These facts suggest that you placed funct (with a t) in a file named func.m . Don't do that. Name the file funct.m

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