Help with my code

Help, I have this code, where I wanted to use 'dsolve to get the answer, but it shows me an 'empty sym' like answer:

clear all
clc

disp('Se resolverá una ecuación integro - diferencial')

syms vel(t) t desp(t)

V = input('Ingrese el voltaje: ' );
l = input('Ingrese la longitud: ');
M = input('Ingrese la masa: ');
B = input('Ingrese la inducción magnética: ');
froz = input('Ingrese la fuerza de rozamiento: ');


eqn = diff(vel,t) == (1/M)*(((V*l*B)-(vel(t)*(l^2)*(B^2)))/(1+(2*int(vel, [0 t])))-froz);
%eqn = diff(vel,t) == 2*int(vel, [0 t])
vel(t) = dsolve(eqn, 'vel(0) = 0')
pretty(vel(t))

What can I do?

[Walter Roberson]

Can you give us some sample inputs for V l M B froz ?

The int() in the equation is going to make it difficult to solve symbolically.

[Alberto Cadena Vaca]

V, l M B and froz are just numbers.

Answer 1

[madhan ravi]

Matlab is having trouble to solve the equation like sir Walter suggests so i converted it into numerical solution:

%SYMBOLIC TO NUMERICAL METHOD 
clear all
clc
disp('Se resolverá una ecuación integro - diferencial')
syms vel(t) 
V = input('Ingrese el voltaje: ' );
l = input('Ingrese la longitud: ');
M = input('Ingrese la masa: ');
B = input('Ingrese la inducción magnética: ');
froz = input('Ingrese la fuerza de rozamiento: ');
vars=vel(t)
eqn = diff(vel,t) == (1/M)*(((V*l*B)-(vel(t)*(l^2)*(B^2)))/(1+(2*int(vel, [0 t])))-froz);
%eqn = diff(vel,t) == 2*int(vel, [0 t])
% vel(t) = dsolve(eqn, 'vel(0) = 0')
% pretty(vel(t))
V = odeToVectorField(eqn)
M = matlabFunction(V,'vars', {'t','Y'})
interval = [0 10];  %time interval
y0 = 0;      %initial conditions
ySol = ode45(M,interval,y0);
tValues = linspace(interval(1),interval(2),1000);
yValues = deval(ySol,tValues,1); %number 1 denotes first solution likewise you can mention 2 & 3 for the next two solutions
plot(tValues,yValues)

%DIRECT NUMERICAL METHOD
V = input('Ingrese el voltaje: ' );
l = input('Ingrese la longitud: ');
M = input('Ingrese la masa: ');
B = input('Ingrese la inducción magnética: ');
froz = input('Ingrese la fuerza de rozamiento: ');
[t,x] = ode45(@(t,x)myod(t,x,V,l,M,B,froz),[0 10],0);
plot(t,x,'-om')

function dxdt = myod(t,x,V,l,M,B,froz)
dxdt =(1/M)*(((V*l*B)-(x(1)*(l^2)*(B^2)))/(1+(2*cumtrapz(x(1))))-froz);
end

An example of the solution graph produced:

[Walter Roberson]

I agree that it is likely that you will need to use numeric methods.

[madhan ravi]

Thank you sir Walter ?

[Hewa selman]

hello sir.

Is this code is suitable for system of integro differential equations?

Answer 2

[Alberto Cadena Vaca]

Help:(

I tried the code but, when I plot the graph, there is just the function x = 0 and don't know why...

[Walter Roberson]

we do not know your inputs

[Alberto Cadena Vaca]

V = 1

B = 1

M = 0.1

l = 0.1

froz = 1

[madhan ravi]

The below is the graph I got with the datas you gave: