SWITCH expression must be a scalar or string constant.

i changed up the file a bit to see if it would run the same and im still getting errors

tspan=[0 25];
y0=[0.1;0;0.2;0];
options=odeset('mass','M(t,y)');
switch options
   case ''
       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)=y0(2);
       p(2)=-(b+a)*sin(y0(1))+M2*l2*(y0(4)^2)*sin(y0(3)-y0(1));
       p(3)=y0(4);
       p(4)=-a*sin(y0(3))-M2*l1*(y0(2)^2)*sin(y0(3)-y0(1));
       m=p;
   case 'mass'
       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(y0(3)-y0(1))];
       c=[0,0,1,0];
       d=[0,M2*l1*cos(y0(3)-y0(1)),0,M2*l2];
       m=[a;b;c;d];
   otherwise
       error(['unknown flag ''' flag '''.']);
end
[t,y]=ode113(m,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')

SWITCH expression must be a scalar or string constant.

Error in GSFE (line 5) switch options

[Stephen23]

A continuation of this question:

http://de.mathworks.com/matlabcentral/answers/233306-combining-function-files-to-one-m-file

Answer 1

[the cyclist]

Your variable options is a struct. A struct cannot be used in that way in a switch statement.

[Muthu Annamalai]

Seems like the questioner is using odeset in wrong format; please refer to

documentation

[Stephen23]

@garrett schander: In fact referring to the documentation would resolve your other question too. Although beginners seem to be allergic to reading the documentation, it does actually explain how functions and operators should be used.

Answer 2

[Walter Roberson]

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

Like I said in another Answer, you are using R11 or earlier.