Prakash J

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How to solve ordinary differemtial equation system with initial conditions and boundary conditions. Here, some initial conditions are unknown variables. So how to find these  values of parameters.

eq1 := diff(f(x), x, x, x)+(1/2)*cos(alpha)*x*(diff(f(x), x, x))+(1/2)*sin(alpha)*f(x)*(diff(f(x), x, x)) = 0;

eq2 := diff(g(x), x, x)+diff(g(x), x)+(diff(g(x), x))*(diff(h(x), x))+cos(alpha)*x*(diff(g(x), x))+sin(alpha)*f(x)*g(x) = 0;

eq3 := diff(g(x), x, x)+diff(h(x), x, x)+1/2*(cos(alpha)*x+sin(alpha)*f(x)) = 0

ics:=f(0)=0, f'(0)=1, f''(0)=a[1], g(0)=1, g'(0)=a[2], h(0)=1, h'(0)=a[3];

bcs:=f(x) , g(x), h(x) tends to 0 ad x tends to infinity

I have some ODE system contains unknown variables with  boundary conditions  (see the attachment). How to solve these system and find the vales of unknown variables.

In this problem, the boundary conditions tends to 0, when x tends to infinity.  BVP_with_parameters.mw
 

restart

eq1 := f(x) = x+a[1]*x^2-(1/48)*sqrt(2)*a[1]*x^4-(1/120)*a[1]^2*sqrt(2)*x^5;

h(x) = -0.3535533905e-3*x^5*a[2]*a[1]*a[3]-0.3333333334e-9*x^5*a[3]*a[2]^4+0.4166666668e-7*x^4*a[2]*a[3]^3-0.3333333334e-9*x^5*a[2]^2*a[3]^3-0.5000000000e-9*x^5*a[3]^2*a[2]^3+0.1250000000e-6*x^4*a[3]*a[2]^3-0.8333333336e-10*x^5*a[2]*a[3]^4+0.1250000000e-6*x^4*a[3]^2*a[2]^2-0.8333333336e-10*x^5*a[2]^5+0.4166666668e-7*x^4*a[2]^4+a[3]*x-0.1473139128e-1*x^4*a[1]*a[3]+0.2946278254e-1*x^4*a[1]*a[2]-0.3240906080e-3*x^5*a[1]*a[2]^2+0.2798964342e-5*x^5*a[2]*a[3]^2+0.4714045206e-5*x^5*a[3]*a[2]^2-0.6629126071e-3*x^4*a[3]*a[2]+0.7812499998e-3*x^5*a[3]-0.2946278254e-1*x^3*a[3]-0.5892556508e-3*x^4*a[2]^2+0.1915080866e-5*x^5*a[2]^3+0.5892556509e-1*x^3*a[2]-0.4687500000e-2*x^5*a[2]+0.5000000000e-2*a[2]^2*x^2-0.1666666667e-4*x^3*a[2]^3+0.5000000000e-2*a[2]*x^2*a[3]-0.3333333334e-4*x^3*a[3]*a[2]^2-0.1666666667e-4*x^3*a[2]*a[3]^2+1.

(1)

bcs := f(0) = 0, (D(f))(0) = 1, f(10) = 0, g(0) = 1, g(10) = 0, h(0) = 1, h(10) = 0;

f(0) = 0, (D(f))(0) = 1, f(10) = 0, g(0) = 1, g(10) = 0, h(0) = 1, h(10) = 0

(2)

sol := dsolve([{f(x), g(x), h(x)}, bcs], numeric)

Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

 

``

 

eq1:=( d)/(dt)u+(d^(2))/(dy^(2))u + s*( d)/(dy)u + delta * theta = 0;

eq2:=( d)/(dt)theta + (d^(2))/(dy^(2))theta + s*Pr*( d)/(dy)theta +lambda* exp(theta/(1 +(epsilon*theta))) = 0; 

initial and boundary conditons   

t <=0; u = theta = 0, for 0 <= y  <= 1   

t> 0;  u =0, theta = 0   at  y = 0;  

t> 0;  u =1, theta = 0   at   y = 1  ;

where, s, epsilon, Pr, lambda, delta are arbitrary parameters

eq1 := diff(f(x), x, x, x)+(1/2)*cos(alpha)*x*(diff(f(x), x, x))+(1/2)*sin(alpha)*f(x)*(diff(f(x), x, x)) = 0;

eq2 := diff(g(x), x, x)+diff(g(x), x)+(diff(g(x), x))*(diff(h(x), x))+cos(alpha)*x*(diff(g(x), x))+sin(alpha)*f(x)*g(x) = 0;

eq3 := diff(g(x), x, x)+diff(h(x), x, x)+1/2*(cos(alpha)*x+sin(alpha)*f(x)) = 0

ics := f(0) = 0, (D(f))(0) = 1, ((D@@2)(f))(0) = a[1], g(0) = 1, (D(g))(0) = a[2], h(0) = 1, (D(h))(0) = a[3];

 

where p, q, r, a are positive constants and phi(0) be a initial condition

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