why is my function not working?

function CMO=ppl (t,y)
a0=30;a1=14;a2=50;a3=20;b3=a3;g=1;
dy1=y(2);
dy2=y(3);
dy3=b3/a0*g-a1/a0*y(3)-a2/a0*y(2)-a3/a0*y(1);
CMO=[dy1;dy2;dy3];

[t,y]=ode23 ('ppl',[0,5],[0,0,0]);% in command window

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

[Adam Danz]

The function works fine for me. Here's the output.

t =
            0
      0.00012
      0.00072
      0.00372
      0.01872
       0.0521
     0.085669
      0.11946
      0.15349
      0.18781
      0.22242
      0.25944
      0.30302
      0.35456
      0.41588
      0.48947
      0.57896
      0.69019
      0.83431
       1.0111
       1.2065
       1.4231
       1.6663
       1.8763
       2.0559
       2.1671
       2.2784
       2.4143
       2.5807
       2.7772
       3.0085
       3.2516
        3.466
       3.6104
       3.7548
       3.8762
       4.0363
       4.2349
       4.4512
       4.6403
       4.7521
       4.8638
            5
y =
            0            0            0
     1.92e-13   4.7999e-09   7.9998e-05
    4.147e-11   1.7278e-07   0.00047992
   5.7184e-09   4.6101e-06    0.0024778
   7.2797e-07   0.00011647     0.012424
   1.5633e-05   0.00089722     0.034288
   6.9163e-05    0.0024117     0.055871
   0.00018664    0.0046604     0.077149
   0.00039404    0.0076442     0.098095
   0.00071816     0.011365      0.11868
    0.0011868     0.015825      0.13888
    0.0018725     0.021354      0.15979
    0.0029627     0.028839      0.18347
    0.0047049     0.038987      0.21006
    0.0075098     0.052786      0.23958
     0.012074     0.071624      0.27177
      0.01962     0.097512      0.30583
     0.032439      0.13352      0.33992
     0.055342      0.18486      0.36971
     0.093934       0.2518      0.38333
      0.15045      0.32579       0.3691
      0.22945      0.40097      0.31954
      0.33567      0.46812      0.22767
      0.43831       0.5054       0.1251
      0.53059      0.51909     0.026645
      0.58837      0.51853    -0.036722
      0.64569       0.5109      -0.1003
      0.71397      0.49205     -0.17632
      0.79299      0.45531     -0.26359
      0.87674      0.39436     -0.35326
      0.95765      0.30276      -0.4329
       1.0178      0.19094      -0.4794
       1.0476      0.08692     -0.48537
       1.0551     0.017718     -0.47062
       1.0528    -0.048289      -0.4413
       1.0438    -0.099847     -0.40612
       1.0228     -0.16026     -0.34662
      0.98468     -0.22029     -0.25569
      0.93188     -0.26341     -0.14163
      0.88015     -0.28017    -0.035751
      0.84875     -0.28065     0.026896
      0.81769     -0.27421     0.088081
      0.78139     -0.25731      0.15893

[madhan ravi]

And the interesting thing is you used ode23 and your error message shows error in ode45 something is fishy here..

Answer 1

[madhan ravi]

change 'ppl' to @ppl

[Adam Danz]

The function also works when the first input is a string that matches a function name. The code Dmitrii shared is functional as-is.

[madhan ravi]

well interesting this is what I got: (version 2018b) if you see https://www.mathworks.com/help/matlab/ref/ode23.html#bu78c6p the last line in input argument says that Data Types should be a function_handle meaning that they have changed it in recent versions (to be noted it's 2018b documentation)

Error using feval
Undefined function or variable 'ppl'.

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

Error in ode23 (line 114)
    odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options,
    varargin);

Error in COMMUNITY (line 1)
[t,y]=ode23 ('ppl',[0,5],[0,0,0]);% in com
 
>> 

[Adam Danz]

Yeah, you're right that it should be a function handle but the string also works in 2018a. Probably a glitch. +1 (upvoted)