undefined variable in a for cycle

In this script (where function is a law of motion function=function(y,y',t)) I would like to find the response of the system varying the parameter 'omega'(included in the function as a force m*g*sin(omega*t))

    [t,x]=ode45(@function,[0 0+dt],[0;0;0;0]);
    plot(omega*ones(Nplot,1), x, '.', 'markersize', 2);
    hold on;

I tried to write a for cycle like:

for w = 10:10:500
  [t,x]=ode45(@function,[0 0+dt],[0;0;0;0]);
  plot(omega*ones(Nplot,1), x, '.', 'markersize', 2);
  hold on;
end,

but if I put omega as a variable of input for 'function' the error that appear is: ??? Input argument "omega" is undefined. how can i do?? thanks a lot!!

[Stephen23]

Never ever use the name function for any function or variable name. The words function is a very important inbuilt key-word, and it should not be shadowed like this. Doing this is going to cause all sorts of problems which you really want to avoid.

In any case you state "if I put omega as a variable of input for 'function'", but your code does not show this at all. How are you defining omega, and how are you providing it to your function?

[Guido De Angelis]

my problem is exactly in the providing 'omega' to the function:

function [ da ] = Lawofmotion( t,a)
[Ks,cs,I,m,g,L,K0,Kc,Icw,c0,cc,T0,r,alfa,mcw,lc,lcw,ls]=deal(1.0e+07,133.58,7.3777e-04,0.105795,9.80665,0.0709444,0.37,1.0e+06,2.7195e-05,9.3e-05,24.22,0.12,0.028284,pi/4,0.11887,0.12,0.010528,0.09);
A=100*g;
h=0.003;
yl=lc*tan(a(1));
dyl=(lc*a(3))/((cos(a(1)))^2);
yc=r*(sin(alfa)-sin(alfa-a(2)));
dyc=r*a(4)*cos(alfa-a(2));
yu=lc*tan(a(1))+h/cos(a(1));
dyu=(((lc+h*sin(a(1)))*a(3)))/((cos(a(1)))^2);
%valore di Fs
if a(1)>=0
    Fs=0;
else 
    Fs=-Ks*ls*a(1)-cs*ls*a(3); %errore cc--cs
end
%valore di R
if yc<yl
    R=lc/cos(a(1));
elseif (yl<yc) && (yc<yu) 
    R=0;
elseif (yl==yc) && (yc==yu) 
    R=0;
elseif (yl==yc) && (yc<yu)
    R=0;
elseif (yl<yc) && (yc==yu)
    R=0;
elseif yc>yu
    R=lc/cos(a(1))+h*tan(a(1));
end
%valore di Fr
if yc<yl
    Fr=Kc*(yl-yc)*cos(a(1))+cc*((dyl-dyc)*cos(a(1))-(yl-yc)*a(3)*sin(a(1)));
elseif (yl<yc) && (yc<yu)
    Fr=0;
elseif (yl==yc) && (yc==yu)
    Fr=0;
elseif (yl==yc) && (yc<yu)
    Fr=0;
elseif (yl<yc) && (yc==yu)
    Fr=0;
elseif yc>yu
    Fr=Kc*(yu-yc)*cos(a(1))+cc*((dyu-dyc)*cos(a(1))-(yu-yc)*a(3)*sin(a(1)));
end
%legge del moto
da=[a(3);a(4);Fs*ls/I-(R*Fr)/(I)-(m*g*A*L*sin(w*t)*cos(a(1)))/I;(-K0*a(2))/Icw-(c0*a(4))/Icw-T0/Icw+(Fr*r*cos(a(1))*cos(alfa-a(2)))/Icw+(mcw*g*lcw*(A*sin(w*t)*cos(a(2))+sin(a(2))))/Icw];

end

in the case in which omega vary in a range of values

[Stephen23]

Sure, I understand that you want "omega" passed to the function. But nowhere outside or inside of the function is "omega" actually defined, so it is not clear if this should be a static constant or something else. Is "omega" supposed to be the loop variable?

[Steven Lord]

Stephen: if you find it possible to create a variable named function or to call a function you've created that is named function, contact Technical Support immediately. The identifier "function" is a keyword, and with one exception (that doesn't apply to "function") you should NOT be able to define variables or call functions with the same name as a keyword.

[Stephen23]

@Steven Lord: I have never tried... but that sounds like an interesting challenge :)

Answer 1

[Stephen23]

If you want to pass extra variables to the function then redefine the function to have three (or more!) inputs:

function da = Lawofmotion(t, a, omega)

and then inside of each loop create an anonymous function which only has two arguments (untested because I don't have dt):

for omega = 10:10:500
    fun = @(t,a) Lawofmotion(t,a,omega);
    [t,x] = ode45(fun, [0,0+dt], [0;0;0;0]);
    ... etc
end

[Guido De Angelis]

perfect! thanks for your help!!