How to get ode45 to work with my function?

I keep getting these error messages:

Undefined function 'mrdivide' for input arguments of type 'function_handle'.

Error in adiabatic (line 35) k = kt*exp((E/R2)*((1/T0)-(1/f)));

Error in odearguments (line 90) f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115) odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in KineticsProject (line 14) [X,V] = ode45(@adiabatic,Xspan,V0)

 if true
function dXdV = adiabatic(V,X)
syms T 
eqn1 = ((CpA+CpB)*(T-T0))+(X*(HRXStand+HvapA+HvapC+(CpC*(T-BPC))+(CpD*(T-T0))-(CpA*(T-BPA))-(CpB*(T-T0)))) == 0;
T = vpasolve(eqn1,T);
f = matlabFunction(T);
k = kt*exp((E/R2)*((1/T0)-(1/f)));
CA = CA0*(1-X);
CB = CA0*(1-X);
rA = k*CA*(CB^0.5); % mol/liter*s
dXdV = rA/FA0;
end

I plugged it into the following code (all variables in eqn1 have been defined):

 if true
Xspan = [0,0.5];
V0 = 0;
[X,V] = ode45(@adiabatic,Xspan,V0)
  end

Answer 1

[Star Strider]

Your code is not easy to follow.

My guess is that this line is throwing the error:

k = kt*exp((E/R2)*((1/T0)-(1/f)));

The most likely solution is to evaluate ‘f’, since that changes it from a function handle to a function evaluation:

k = kt*exp((E/R2)*((1/T0)-(1/f(X))));

[Bryan Lee]

I'm sorry. The bulk of the code is just defining variables. The important parts of the code are after 'syms T'.

I know that I have to somehow convert the symbolic equation T(X) into a numerical form so that it can be evaluated by ode45, but I can't figure out how.

[Star Strider]

I thought I told you exactly how in my Answer:

k = kt*exp((E/R2)*((1/T0)-(1/f(X))));

[Bryan Lee]

I tried it and it did not work

[Star Strider]

What does ‘did not work’ mean?

[Bryan Lee]

Thank you for the prompt responses. These are the errors I get:

Error using symengine>@()1.123e3 Too many input arguments.

Error in adiabatic (line 35) k = kt*exp((E/R2)*((1/T0)-(1/f(X))));

Error in odearguments (line 90) f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115) odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in KineticsProject (line 14) [X,V] = ode45(@adiabatic,Xspan,V0)

[Star Strider]

I would use the Symbolic Math Toolbox once to create any functions you need, extract them as anonymous functions with matlabFunction, then do all the calculations numerically.

[Bryan Lee]

Thank you for your help Start Strider. Although I fixed it a different way, your guidance pointed me in the right direction. I was able to resolve this problem without using matlabFunction. I used double() to convert my symbolic expression obtained from vpasolve() into double precision and ode45 accepted it. Thank you!

[Star Strider]

My pleasure.

If my Answer helped you solve your problem, please Accept it!