Why is my index becoming zero when using a driver program to run ode45?

This will probably be a glaring issue that I am missing. If I am trying to integrate from 0 to 0.115 why is my index coming back 0? Code is included below. I do not claim to be very good with MATLAB yet, either.

Solver:

function dydx = finPFR(x,y)
global beta gamma
dydx = zeros(2,1);
c = y(1);
T = y(2);
dydx(1) = -c*exp(gamma(1-(1/T)));
dydx(2) = c*beta*exp(gamma(1-(1/T)));
end

And the driver program:

global beta gamma
beta = 0.15;
gamma = 30;
xstep = [0:0.001:0.115];
yzero = [1 1];
[myx,myy] = ode45(@finPFR,xstep,yzero);
subplot(2,1,1)
plot(myx,myy(:,1,'k--'))
xlabel('VR/Q')
ylabel('Conversion')
subplot(2,1,2)
plot(myx,myy(:,2,'k-'))
xlabel('VR/Q')
ylabel('Temperature')

Errors:

>> run_finPFR
Attempted to access gamma(0); index must be a positive integer or
logical.

Error in finPFR (line 6)
dydx(1) = -c*exp(gamma(1-(1/T)));

Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ode45 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs,
odeFcn, ...

Error in run_finPFR (line 6)
[myx,myy] = ode45(@finPFR,xstep,yzero);

I know it's a long shot, but I have spent hours on this and can't seem to figure out where I am going wrong with the index. Any help would be appreciated!

[arun]

Can u pls post the equations ur using for this problem

[Aaron Tytschkowski]

This is for a plug flow reactor. The equations we are given are:

dc/dtheta = -c*exp(gamma*(1-1/T))

and

dT/dtheta = beta*c*exp(gamma*(1-1/T))

Theta is "residence" or "hold up" time

Answer 1

[Walter Roberson]

dydx(1) = -c*exp(gamma*(1-(1/T)));
dydx(2) = c*beta*exp(gamma*(1-(1/T)));

Note: using gamma as a variable is easily confused with the gamma function and so is not recommended.

[Aaron Tytschkowski]

I believe this has solved the original issue, thanks! Unfortunately now my index is exceeding my matrix, but I cant seem to change my code to account for this..

[Walter Roberson]

Please show the current code and the traceback of the new error.

[Aaron Tytschkowski]

Driver:

global beta Gam
  beta = 0.15;
  Gam = 30;
  xstep = [0:0.001:0.115];
  yzero = [1 1];
  [myx,myy] = ode45(@finPFR,xstep,yzero);
  subplot(2,1,1)
  plot(myx,myy(:,1,'k--'))
  xlabel('VR/Q')
  ylabel('Conversion')
  subplot(2,1,2)
  plot(myx,myy(:,2,'k-'))
  xlabel('VR/Q')
  ylabel('Temperature')

Solver:

function dydx = finPFR(x,y)
global beta Gam
dydx = zeros(2,1);
c = y(1);
T = y(2);
dydx(1) = -c*exp(Gam*(1-(1/T)));
dydx(2) = c*beta*exp(Gam*(1-(1/T)));
end

Error:

>> run_finPFR
Index exceeds matrix dimensions.

Error in run_finPFR (line 8)
plot(myx,myy(:,1,'k--'))

I can't seem to find why I am causing the matrix to be over filled. Thought it might be my xstep, but changing it didn't fix the problem. Thanks again for taking the time to look this over!

[Walter Roberson]

plot(myx,myy(:,1),'k--')

You had the ) in the wrong place and were trying to index myy by 'k--'

[Aaron Tytschkowski]

You are a life saver. I am new to MATLAB and am not fluent in code and how it works quite yet. Thank you so much! This saves me a lot of time.