solutions =
Problems plotting an implicit solution to a differential equation
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I am trying to plot the implicit solution to a differential equation, but fimplicit comes up with an error. The code is
clear all
syms y(x)
eqn = diff(y) == (2*x+y+2)/(2*x+y-4);
solutions = dsolve(eqn,Implicit=true)
impl = subs(solutions(1),[sym("C1"),x],[0,x])
fimplicit(impl)
The solution to the differential equation is correct. I am afraid I don't understand the error message for fimplicit...
采纳的回答
For more complicated cases where an explicit solution cannot be found:
syms y(x)
eqn = diff(y) == (2*x+y+2)/(2*x+y-4);
solutions = dsolve(eqn,Implicit=true)
syms u
impl1 = subs(lhs(solutions(1))-rhs(solutions(1)),[sym("C1"),y],[0,u]);
[impl2,~] = numden(lhs(solutions(2)));
impl2 = subs(impl2,y,u);
impl1 = matlabFunction(impl1,'Vars',[x,u])
impl2 = matlabFunction(impl2,'Vars',[x,u])
hold on
fimplicit(impl1)
fimplicit(impl2)
hold off
grid on
更多回答（1 个）
syms y(x)
eqn = diff(y) == (2*x+y+2)/(2*x+y-4);
solutions = dsolve(eqn,x)
impl1 = subs(solutions(1),[sym("C1"),x],[0,x])
impl2 = solutions(2)
fplot([impl1, impl2], [1 3.5])
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