symbolic function to numeric value

I have used this code to solve second order different equaion.Now I want to get all the value of j1 from 0 to 30. the answer comes in terms of T,how do i put numerical value of t to obtianed equation amd store those numerical values?
syms j1(t) 
Dj1=diff(j1);
ode = (20*diff(j1,t,2)+20*diff(j1,t)+100*j1)==f1;
cond1=j1(0)==0;
cond2=Dj1(0) == 0;
conds=[cond1,cond2];
j1Sol(t)=dsolve(ode,conds);
j1Sol=simplify(j1Sol);

Answer 1

[Star Strider]

First, ‘f1’ has to appear somewhere before it is used.

With that correction, try this:

syms j1(t) f1 
Dj1=diff(j1);
ode = (20*diff(j1,t,2)+20*diff(j1,t)+100*j1)==f1;
cond1=j1(0)==0;
cond2=Dj1(0) == 0;
conds=[cond1,cond2];
j1Sol(t)=dsolve(ode,conds);
j1Sol=simplify(j1Sol, 'Steps',100);
j1Sol_fcn = matlabFunction(j1Sol, 'Vars',{t, f1});

f1 = 42;
t = linspace(0, 42, 420);

figure
plot(t, j1Sol_fcn(t,f1))
grid

See the documentation on matlabFunction for details on how to use it.

[Madhav rijal]

i want to have all the values of j1 for later use.How do i store those values,not the plot. Thanks so much for you help. If i assign f1=j1sol_fcn(t,f1),it gives the syms relation. i want its values,Numbers. Plz help.

[Madhav rijal]

oo it worked out when gave value of t after describing j1sol_fcn.I had assigned t and f in the begining.Thanks tons

[Madhav rijal]

clear
clc
a1=1;
a2=2;
i=0;
for t=0:30
    i=i+1;
    if t<10
        f1=0;
        f2=0;
    end
    
    if t>=10&&t<11
        f1=a1*(1-cos(pi*t));
        f2=a2*(1-cos(pi*t));
    end
   
    if t>=11&& t<20
        f1=2*a1;
        f2=2*a2;
    end
    if t>=20 && t<21
        f1=a1*(1+cos(pi*t));
        f2=a2*(1+cos(pi*t));
    end
    
    if t>=21
        f1=0;
        f2=0;
    end
    
    f1_list(:,i)=[f1];
    f2_list(:,i)=[f2];
    
    %solving impedence
syms j(t1) f 
Dj=diff(j);
ode = (20*diff(j,t1,2)+20*diff(j,t1)+100*j)==f;
cond1=j(0)==0;
cond2=Dj(0) == 0;
conds=[cond1,cond2];
jSol(t1)=dsolve(ode,conds);
jSol=simplify(jSol, 'Steps',100);
jSol_fcn = matlabFunction(jSol, 'Vars',{t1, f1});
t1=[t];
f=f1;
j1=j1Sol_fcn(t1,f);
j1_list(:,i)=j1;
f=f2;
j2=j1Sol_fcn(t1,f);
j2_list(:,i)=j2;
end

this is what i am trying to do
Error using sym/matlabFunction>getOptions (line 656)
The value of 'Vars' is invalid. 'Vars' value must be a character vector, a 1-dimensional cell array of character vectors, a 1-dimensional cell array of symbolic variables or arrays of symbolic
variables, or an array of symbolic variables.

Error in sym/matlabFunction (line 154)
opts = getOptions(args);

Error in force_control (line 44)
jSol_fcn = matlabFunction(jSol, 'Vars',{t1, f1});
  Got this

[Star Strider]

After a few edits, this appears to work:

a1=1;
a2=2;
i=0;
tv=0:30;
for k = 1:numel(tv)
    t = tv(k);
    i=i+1;
    if t<10
        f1=0;
        f2=0;
    end
    
    if t>=10&&t<11
        f1=a1*(1-cos(pi*t));
        f2=a2*(1-cos(pi*t));
    end
   
    if t>=11&& t<20
        f1=2*a1;
        f2=2*a2;
    end
    if t>=20 && t<21
        f1=a1*(1+cos(pi*t));
        f2=a2*(1+cos(pi*t));
    end
    
    if t>=21
        f1=0;
        f2=0;
    end
    
    f1_list(:,i)=[f1];
    f2_list(:,i)=[f2];
    
    %solving impedence
syms j(t1) f t1 
Dj=diff(j);
ode = (20*diff(j,t1,2)+20*diff(j,t1)+100*j)==f;
cond1=j(0)==0;
cond2=Dj(0) == 0;
conds=[cond1,cond2];
jSol(t1)=dsolve(ode,conds);
jSol=simplify(jSol, 'Steps',100);
j1Sol_fcn = matlabFunction(jSol, 'Vars',{t1, f});
t1=[t];
f=f1;
j1=j1Sol_fcn(t1,f);
j1_list(:,k)=j1;
f=f2;
j2=j1Sol_fcn(t1,f);
j2_list(:,k)=j2;
end

The code is not very efficient, however I am not certain what you are doing, so the only changes I made to it were those necessary to get it to run.

Consider possibly putting the ODE code before the loop, and using the 'Vars' name-value pair to add the appropriate arguments to it. Then substitute the appropriate arguments to ‘j1Sol_fcn’ in the loop to get ‘j1’ rather than creating ‘j1Sol_fcn’ in each iteration of the loop.

.