title: solving a system of 6 differential equations by ODE45 in matlab
body: <p>I am trying to solve a system of 6 differential equations using matlab. I created a set of 6 differential equations as follows in a function m file named as Untitled.m</p>
  
  <pre><code>function ydot=Untitled(z,y)
  ydot = zeros(6,1);
  %y(1)=A
  %y(2)=B
  %y(3)=C
  %y(4)=D
  %y(5)=P
  y(6)=T
  
  A=0.50265
  k11=(333/106.7)*1.15*1000*exp(-59660/(8.314*960))
  k31=(333/40)*73.6*exp(-47820/(8.314*960))
  k32=(333/14.4)*1.79*exp(-30950/(8.314*960))
  k21=(106.7/40)*426*exp(-68830/(8.314*960))
  k22=(106.7/14.4)*0.000599*exp(-57740/(8.314*960))
  Pcat=1450
  g=9.81
  phi=exp(-al*tc)
  al=59100*exp(-67210/(8.314*T))
  tc=(0.50265*1450*33)/143.64
  H11=393000
  H31=795000
  H32=1200000
  H21=1150000
  H22=151000
  E=1-((285.765*17.56)/((6.1*1450)+(17.56*285.765)))
  Fcat=143.64
  Cpcat=1087
  Cp=1000*(y(1)*3.3+y(2)*3.3+y(3)*3.3+y(4)*1.087)
  F=19.95
  ydot(1)= -(A*(1-E)*Pcat*(k11+k31+k32)*phi*y(1)*y(1))/F
  ydot(2)=  (A*(1-E)*Pcat*(k11*y(1)*y(1)-(k21+k22)*y(2))*phi)/F
  ydot(3)=  (A*(1-E)*Pcat*(k31*y(1)*y(1)+ k21*y(2))*phi)/F
  ydot(4)=  (A*(1-E)*Pcat*(k32*y(1)*y(1)+k22*y(2))*phi)/F
  ydot(5)= -(Pcat*g*(1-E))
  ydot(6) = ((phi*(1-E)*Pcat*A)*(y(1)*y(1)((k11*H11)+(k31*H31)+(k32*H32))+y(2)((k21*H21)+    (k22*H22)))/((F*Cp)+(Fcat*Cpcat)))
  
  
  %UNTITLED Summary of this function goes here
  %   Detailed explanation goes here
  </code></pre>
  
  <p>then i have created another file for using the ODE45 solver to solve the equations</p>
  
  <pre><code>function main
  options = odeset('RelTol',1e-6); %,'AbsTol',[1e-5 1e-5 1e-5 1e-5 1e-5 1e-5 ]);
  Y0=[1.0;0.0;0.0;0.0;180000.0;959.81]
  zspan=0:0.5:33;
  [z,y]= ode45(@Untitled,zspan,Y0,options);
  figure
  hold on
  plot(z,y(:,1));
  plot(z,y(:,2),':');
  </code></pre>
  
  <p>but I am getting errors </p>
  
  <pre><code>??? Error using ==&gt; feval
  Error: File: Untitled.m Line: 41 Column: 37
  ()-indexing must appear last in an index expression.
  Error in ==&gt; odearguments at 110
  f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
  Error in ==&gt; ode45 at 173
  [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
  Error in ==&gt; ode at 6
  [z,y]= ode45(@Untitled,zspan,Y0,options);
  </code></pre>
  
  <p>could anyone please help me with this as it is really important for me and i am new to MATLAB</p>
  
  <p>thanx in advance :)</p>