# Singularity in NDSolve?

Posted 10 months ago
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 Hi, I am trying to plot the angles of a spherical pendulum fixed to a oscillating cart. I have derived the equations of motion, when I try to solve the equations using "NDSolve", following error occurs: NDSolve::ndsz: At t == 0.1374350849846401, step size is effectively zero; singularity or stiff system suspected. Have you got an idea? (*Equations of motion for spherical pendulum fixed to oscillating cart*) Remove[x, L, w , A] (*Define equations of motion*) eq1 = θ''[t] - ρ'[t]^2*Sin[θ[t]]*Cos[ρ[t]] - x''[t]/L*Cos[θ[t]]*Cos[ρ[t]] - (g*Sin[θ[t]])/L; eq2 = L*x''[t]*Sin[θ[t]]*Sin[ρ[t]] - L^2*Sin[θ[t]]*(ρ''[t]*Sin[ρ[t]] + 2*ρ'[t]^2*Cos[ρ[t]]); eq3 = -A*w^2*Cos[w*t] - x''[t]; (*x is the cart-position, θ and ρ the angles of the pendulum*) (*Give numerical values for constants*) A = 1; g = 9.81; L = 1; w = 7; (*Solve the equations using NDSOlve*) sol = NDSolve[{eq1 == 0, eq2 == 0, eq3 == 0, θ[0] == 1, θ'[0] == 0, ρ[0] == 1, ρ'[0] == 0, x[0] == 0, x'[0] == 0}, {θ, ρ}, {t, 0, 10}]; Plot[{Evaluate[θ[t] /. sol], Evaluate[ρ[t] /. sol]}, {t, 0, 10}] `