MATLAB: How to assign values to the variables using “dsolve” for solving first order ODE Equations simultaneously

assignmentdsolveodevariable

I am using "dsolve" to solve my first order ode .The function "dsolve" works fine but it does not allow assigning values to the variables. My code is given as follows.
%Parameters clear all; syms A Epsilon0 k1 k2 e s d R s f T c0 ; A=0.5*10^(-9); Epsilon0=8.85*10^-12; k1=10; k2=10; e=1.6*10^-19; s = 1.8*10^(-9);%m gap size% d=3*s; % total distance R=1; t=0:(0.0001*10^-3):(0.5*10^-3); f=10000; v0=7.5; T=5/f; v=v0*sin(2*pi*f*t); plot(t,v); c0=(A*Epsilon0*k1)/d;
inits='q(0)=(20*10^(-20)),Q(0)=0'; [q,Q]=dsolve('Dq=((v/R)-(1/R)*(((d*q)+(s*Q))/(c0*d)))','DQ=(((q+Q)/(A*Epsilon0*k1))*s)',inits);
OUTPUT q =
(c0*d*exp((s*t)/(2*A*Epsilon0*k1)……………………………………..(this is so long expression).
Issue: In the above out, the variables are used instead of the values i have assigned and initialized in the code .
Requirement : I need these variables to be replaced by the values i have assigned to them.

Best Answer

AK, use the subs command. I also recommend differentiating between the symbolic variables and their numeric values, e.g. A versus An .
 syms A Epsilon0 k1 k2 e s d R s f T c0
 An        = 0.5*10^(-9);
 Epsilon0n = 8.85*10^-12;
 k1n       = 10;
 k2n       = 10;
 en        = 1.6*10^-19;
 sn        = 1.8*10^(-9);%m gap size%
 dn        = 3*s; % total distance
 Rn        = 1;
 inits = 'q(0)=(20*10^(-20)),Q(0)=0';
 [q,Q] = dsolve('Dq=((v/R)-(1/R)*(((d*q)+(s*Q))/(c0*d)))','DQ=(((q+Q)/(A*Epsilon0*k1))*s)',inits);
 qn    = vpa(subs(q,{A,Epsilon0,k1,k2,e,s,d,R},{An,Epsilon0n,k1n,k2n,en,sn,dn,Rn}),3);
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