combining function files to one .m file

Question

garrett schander 2015-8-11

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评论： Stephen23 2015-8-12

hi everyone, my question is on how to combine function files.

i am running a plot vs time on a double pendulum and i haven't been able to get the script to run without having it run off 4 files. But for submission i have to submit it in one function file

function varargout=dp_S(t,y,flag)
switch flag
case '' 
 varargout{1}=dp_p(t,y);
case 'mass' 
 varargout{1}=dp_m(t,y);
otherwise
 error(['unknown flag ''' flag '''.']);
end
function m =dp_m(t,y)
M1=1;
M2=1;
g=9.81;
l1=1;
l2=1;
a=[1,0,0,0];
b=[0,(M1+M2)*l1,0,M2*l2*cos(y(3)-y(1))];
c=[0,0,1,0];
d=[0,M2*l1*cos(y(3)-y(1)),0,M2*l2];
m=[a;b;c;d]; 
function p= dp_p(t,y) 
M1=1;
M2=1;
g=9.81;
l1=1;
l2=1;
a=M2*9.81;
b=M1*9.81;
p=zeros(4,1);
p(1)=y(2);
p(2)=-(b+a)*sin(y(1))+M2*l2*(y(4)^2)*sin(y(3)-y(1));
p(3)=y(4);
p(4)=-a*sin(y(3))-M2*l1*(y(2)^2)*sin(y(3)-y(1));
tspan=[0 25];
y0=[0.1;0;0.2;0]; 
options=odeset('mass','M(t,y)');
[t,y]=ode113('dp_S',tspan,y0,options);
subplot(2,1,1)
plot(t,y(:,1))
grid
xlabel('Time')
ylabel('Theta1')
subplot(2,1,2)
plot(t,y(:,3))
grid
xlabel('Time')
ylabel('Theta2')

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Stephen23 2015-8-12

This question is continued here:

http://de.mathworks.com/matlabcentral/answers/233334-switch-expression-must-be-a-scalar-or-string-constant

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Answer 1

Walter Roberson 2015-8-12

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If that code is working when it is in separate files then you must be using MATLAB 5.3 (R11) or earlier, as the ode solvers worked differently before function handles were introduced. Documentation for such an early version is not readily available; I do not know if any of the regular volunteers keeps such an early version on hand.

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Walter Roberson 2015-8-12

You are using Release 11 (R5.3) syntax. It hasn't been valid since 2000.

http://www.mathworks.com/matlabcentral/answers/94154-why-do-i-receive-an-error-about-a-switch-expression-when-using-ode15s-within-matlab

Stephen23 2015-8-12

编辑：Stephen23 2015-8-12

在 MATLAB Online 中打开

The ode113 documentation clearly states that its first argument is " odefun A function handle that evaluates the right side of the differential equations", whereas you are providing it with a string like this:

ode113('dp_S',...

As Walter Roberson has tried to point out to you, this has not been a valid syntax for years and years... the best solution is to read the documentation.

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