SWITCH expression must be a scalar or string constant.

Question

garrett schander 2015-8-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/233334-switch-expression-must-be-a-scalar-or-string-constant

编辑： Stephen23 2015-8-12

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

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Stephen23 2015-8-12

A continuation of this question:

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

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Answer 1

the cyclist 2015-8-12

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/233334-switch-expression-must-be-a-scalar-or-string-constant#answer_189022

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

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Muthu Annamalai 2015-8-12

编辑：Walter Roberson 2015-8-12

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

documentation

Stephen23 2015-8-12

编辑：Stephen23 2015-8-12

@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.

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