Mass Matrix SWITCH Problem in Matlab
1 次查看(过去 30 天)
显示 更早的评论
I'm having a problem with my ODE in Matlab. The code to start the ODE solver is the following:
refine = 4;
options = odeset('Refine', refine,...
'RelTol', 1e-9,'absTol',1e-9*ones(1,length(y_sym)),'Mass',Mss_bend,'MassSingular','no','MstateDependence','strong')
[t_bend_i,y_bend_i] = ode45(@(t,y) ...
bending_DGL(t,y,time_r,dt,ug,vg,Mss_bend,Fss_bend,Sys,flag),time_r_i,IC_bend_i,options);
And the corresponding function file containing the ODE is:
function dy = bending_DGL(t,y,time_r,dt,ug,vg,Mss_bend,Fss_bend,Sys,flag)
r = Sys.r;
roh = Sys.roh;
A = Sys.A;
I = Sys.I;
ne = Sys.ne;
nnode = Sys.nnode;
ndof = Sys.ndof;
Le = Sys.Le;
E = Sys.E;
g = Sys.g;
EI = E*I;
EA = E*A;
%Interpolate Earthquake Excitation
i = floor(t/dt) + 1;
if i < length(time_r)
u = ug(i) + (t-time_r(i))/(time_r(i+1)-time_r(i))*(ug(i+1)-ug(i));
v = vg(i) + (t-time_r(i))/(time_r(i+1)-time_r(i))*(vg(i+1)-vg(i));
else
u = 0;
v = 0;
end
%Load State Space Representation of Problem
switch flag
case ''
dy = Fss_bend;
case 'mass'
dy = Mss_bend;
end
Now I'm trying to solve the ODE where Mss_bend is the mass matrix which is symbolic, because it is statedependent so Mss_bend(y,t) and Fss_bend(y,t) is the right side of the Equation which is state dependent too. So now I wan't to solve the Problem Mss_bend(y,t)*dy = Fss_bend where dy is the derivative of the vector y with respect to time.
When I start the calculation it gives me the
Error: Switch expression must be a scalar or string constant.
Error in bending_DGL (line 31)
switch flag
Error in @(t,y)bending_DGL(t,y,time_r,dt,ug,vg,Mss_bend,Fss_bend,Sys,flag)
Error in odearguments (line 87)
What did i do wrong? Is there a problem because the matrices are symbolic?
Matlab tell's me in the function file that y is unused:
function dy = bending_DGL(t, y,time_r,dt,ug,vg,Mss_bend,Fss_bend,Sys,flag
How do I solve this Problem. y is as symbolics in the Mss_bend and Fss_bend where y(1), y(2) etc is declared as symbols.
Thank you for your answers!
回答(4 个)
Walter Roberson
2016-4-7
We would need to see how you initialized your flag variable to figure out why you are getting the error for switch.
You will need to change your code anyhow. Assuming that your Fss_bend and Mss_bend are expressions rather than functions:
%Load State Space Representation of Problem
switch flag
case ''
dy = double( subs(Fss_bend, {sym('t', sym('y')}, {t, y}) );
case 'mass'
dy = double( subs(Mss_bend, {sym('t', sym('y')}, {t, y}) );
end
However, it seems likely that your Mss_bend and Fss_bend also use some of the variables that you compute, such as u and v. We need to know whether Mss_bend and Fss_bend are functions or expressions, and if they are functions we need to know the order they expect their arguments in. If they are expressions then we need to know which symbolic variables need to be substituted.
7 个评论
Torsten
2016-4-8
Maybe
dy = double( subs(Fss_bend, {sym('u'), sym('v'), sym('y')}, {u, v, y'}) );
?
Best wishes
Torsten.
Marius
2016-4-21
13 个评论
Walter Roberson
2016-4-23
What is your FssFun reshape()'ing to? It should be reshaping to a column vector.
If you are using matlabFunction(something) to generate FssFun then use matlabFunction(something(:))
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!