Using ODE45 for chemical reactions: Error using VERTCAT

I have a system of ODEs for a system of chemical reactions and I can't seem to find the route of this error: Error using VERTCAT. Simply can't work out why the dimensions are not constant.

Here is the code that defines the reactions:

function dcdt = reactions(t,c)
global k1 k2 k3 k4 k5 k6 k7
% REACTIONS
% 1. [A] + hv  -k1-> [A] + [B]
% 2. [B] + [C] -k2-> [D]
% 3. [D] + hv  -k3-> [C] + [E]
% 4. [C] + [E] -k4-> [D]
% 5. [B] + [B] -k5-> [B]
% 6. [B] + [D] -k6-> [F]
% 7. [B] + [D] -k7-> [G]
% ODE
% d[A]/dt = -k1[A][hv] + k1[A][hv]
% d[B]/dt =  k1[A][hv] - k2[B][C]  - k5[B][B] - k5[B][B] + k5[B][B] - k6[B][D] - k7[B][D]
% d[C]/dt = -k2[B][C]  + k3[D][hv] - k4[C][E]
% d[D]/dt =  k2[B][C]  - k3[D][hv] + k4[C][E]  - k6[B][D] - k7[B][D]
% d[E]/dt =  k3[D][hv] - k4[C][E] 
% d[F]/dt =  k6[B][D]
% d[G]/dt =  k7[B][D]

dcdt = [-k1*c(1)*1 + k1*c(1); ...
         k1*c(1)*1 - k2*c(2)*c(3) - k5*c(2)*c(2) - k5*c(2)*c(2) + k5*c(2)*c(2) - k6*c(2)*c(4) -k7*c(2)*c(4); ... 
        -k2*c(2)*c(3) + k3*c(4)*1 - k4*c(3)*c(5); ...
         k2*c(2)*c(3) -k3*c(4)*1 + k4*c(3)*c(5) - k6*c(2)*c(4) - k7*c(2)*c(4); ...
         k3*c(4)*1 - k4*c(3)*c(5); ...
         k6*c(2)*c(4); ...
         k7*c(2)*c(4)];

The main file reads:

% globals
global k1 k2 k3 k4 k5 k6 k7;

% Set rates
k1 = 1;
k2 = 2;
k3 = 3;
k4 = 4;
k5 = 5;
k6 = 6;
k7 = 7;

% Set duration
tspan = [0 100];

% Initial concentrations
c0 = [1 2 3 4 5 6 7];

% define method
[t,c] = ode45('grs', tspan, c0);

Most probably something silly but it has me stumped. I know the ODE can be slightly simplified but I'm not sure why this would cause the problem. Does anyone have any insight? Or a link to a good tutorial that will put me back on the right path?

Thanks in advance for any help you can provide, Dan

Answer 1

[Walter Roberson]

Change your line

k1*c(1)*1 - k2*c(2)*c(3) - k5*c(2)*c(2) - k5*c(2)*c(2) + k5*c(2)*c(2) - k6*c(2)*c(4) -k7*c(2)*c(4)

to

k1*c(1)*1 - k2*c(2)*c(3) - k5*c(2)*c(2) - k5*c(2)*c(2) + k5*c(2)*c(2) - k6*c(2)*c(4) - k7*c(2)*c(4)

Notice the extra space after the last negative sign. With the spacing you had, the parser was interpreting the line as designating a row with two values, the first one being (k1*c(1)*1 - k2*c(2)*c(3) - k5*c(2)*c(2) - k5*c(2)*c(2) + k5*c(2)*c(2) - k6*c(2)*c(4)) and the second one being (-k7*c(2)*c(4))

Unary minus binds more tightly than subtraction.

[Dan Pearce]

Thanks for your time Walter.

Made that change but still get the same error...is this my mistake? Or something else you can see that looks crooked?

Dan

[Walter Roberson]

4th line, second term, "-k3*c(4)*1" with no space after the "-"

[Dan Pearce]

Thanks again Walter. I had a feeling it would be something this silly!