MATLAB: CAT arguments dimensions are not consistent Error in Solving ode45

odeode45

I am getting the CAT argument dimensions error in computing two differential equations using ODE45. Apparently everything seems right and the vector I used seem to have same dimentions. The code is Give below.

 % The memcapfinal.m includes the follwing code.
 function qprime=memcapfinal(t,q);
 e = 1.6*10^(-19); %C electron charge%
 h = 6.63*10^(-34); %J/s planks constant%
 phi = (0.3)*1.6*10^(-19); %J barrier height%
 R=1;
 Epsilon0 = 8.85*10^-12;
 k1       = 100;
 k2       = 10;
 d=10*10^(-9);
 s = 6*10^(-9);
 m = 9.11*10^(-31); %kg electron mass%
 A = 10^(-4);
 b = -4*3.14*s/h;
 c0=(A*Epsilon0*k1)/d;
 t1=0:0.0000001:0.0005;
 f=10000;
 v0=7.5;
 T=5/f;
 v=v0*sin(2*3.14*f*t1);
 plot(t1,v);
 qprime=[((v/R)-(1/R)*(((d*q(1))+(s*q(2)))/(c0*d)));(sqrt(2*m*phi)/s*(e/h)^2*(((q(1)+q(2))/(2*A*Epsilon0*k2))*s)*exp(b*sqrt(2*m*phi)))*A];

And the code which calls the ODE is given below

 clear all;
 q0=[0 10^(-9)];
 tspan1=[0,0.0005];
 [t,q]=ode45(@memcapfinal,tspan1,q0)
 subplot(2,1,1)
 plot(t,q(:,1))
 subplot(2,1,2)
 plot(t,q(:,2))

Best Answer

dbstop if caught error

then run the program. If it stops for any reason other than the cat problem, then use dbcont to keep going.

When it stops with the cat error, display

size( ((v/R)-(1/R)*(((d*q(1))+(s*q(2)))/(c0*d))) )
size( (sqrt(2*m*phi)/s*(e/h)^2*(((q(1)+q(2))/(2*A*Epsilon0*k2))*s)*exp(b*sqrt(2*m*phi)))*A )

As you do not appear to use t in your calculation, and as your code would error if q did not have at least 2 elements, I predict that the problem happens every time

Related Solutions

MATLAB: Undefined variable while computing ode45 in matlab and issue with the vector lengths after computing ode.

You are creating v in the workspace of the function memcapfinal. Variables defined in function workspaces disappear when the function returns, except under some limited conditions

the variable is marked as persistent in the function. In this case the variable continues to exist until the function is "clear"'d from memory, but the variable is not accessible from outside the function (at least not without difficulty)
the variable is marked as global in the function. In this case the variable would be available to any other function or script that used "global" with the same variable name
a reference to the variable is created in an anonymous function and the anonymous function is returned out of the function
some cases involving handle objects and static objects

In addition, the value of a variable might get saved away in an accessible location

by using the seldom-recommended assignin
by assigning the value to a UserData field of an object
by using setappdata() including by way of guidata()

If you try any of these, you will quickly encounter the problem that the "v" you manage to retrieve is a scalar. Because every call you use to save it out from your function will overwrite the previous version. For the purposes of your plotting what you want is to save all of the values. That requires you to be a bit more clever about what you save and where.

MATLAB: 2 coupled second order equations

Bellow is the code with 2 methods.

Observation: piecewise RUNGE-KUTTA method is more accurate whenever the trajectory is orbital around the attractor (0,0)

% S(t) := T(t) / W(t), 
% S(t) = s(i) for tbin(i) <= t < tbin(i+1); 
%

n = 10; % number of interval where S is constant
tbin = [0 cumsum(0.1+rand(1,n))];
s = rand(1,n);
s(end+1) = s(end);
q0 = rand(4,1);
% Cauchy condition
tspan = tbin([1 end]);
[t,q] = ode15s(@(t,q) odefun(t,q,tbin,s), tspan, q0);
x = q(:,1);
y = q(:,3);
plotsol(1,t,x,y,tbin,'single run ode15s');
%
t = [];
q = [];
for k=1:n
    subts = tbin([k k+1]);
    [tk,qk] = ode45(@(t,q) odefun(t,q,tbin,s), subts, q0);
    t = [t; tk];
    q = [q; qk];
    q0 = q(end,:);
end
x = q(:,1);
y = q(:,3);
plotsol(2,t,x,y,tbin,'piecewise ode45');
function plotsol(fignum,t,x,y,tbin,str)
% plot the solution
fig = figure(fignum);
clf(fig);
% make figure wider
p = get(fig,'position');
p(3) = 800;
set(fig,'position',p);
subplot(1,2,1),
h = plot(t,[x,y]);
xlabel('t');
hold on
n = length(tbin);
for k=2:n
    plot(tbin(k)+[0 0],ylim(gca),'-.k');
end
legend(h,'x','y');
title(str);
subplot(1,2,2),
plot(x,y);
xlabel('x');
ylabel('y');
title(str);
end
function qp = odefun(t,q,tbin,s)
x = q(1);
xp = q(2);
y = q(3);
yp = q(4);
[~,i] = histc(t,tbin);
S = s(i);
a = sqrt(x.^2+y.^2).^3;
b = sqrt(xp.^2+yp.^2);
c = S./b;
xpp = -x./a + xp.*c;
ypp = -y./a + yp.*c;
qp = [xp; xpp; yp; ypp];
end

Best Answer

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MATLAB: Undefined variable while computing ode45 in matlab and issue with the vector lengths after computing ode.

MATLAB: 2 coupled second order equations

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