# Getting error ParametricNDSolve::ndnum: from ParametricNDSolve

arec = 1/1100;
aeq = 1/(2.4*10^4*0.13);
alpha = (arec/aeq)^1/2;
y = (alpha*x)^2 + 2*alpha*x;
yb = y*(0.02/0.13);
yc = y*(0.11/0.13);
xi = 10^-3;
xrec = (((alpha^2 + 1)^1/2) - 1)/alpha;
n = 2*alpha*(alpha*x + 1)/((alpha*x)^2 + 2*alpha*x);
n0 = 2*alpha*(alpha*xi + 1)/((alpha*xi)^2 + 2*alpha*xi);

c =
ParametricNDSolve[
{phi'[x] == -n*phi[x] + ((3*n^2/2*k)*(vg[x] (4/3 + y + yc) + vc[x]*yc[x])/(1 + y)),
dc'[x] == -k*vc[x] + 3*phi'[x], vc'[x] == -n*vc[x] + k*phi[x],
dg'[x] == -(3/4)*k*vg[x] + 4*phi'[x],
vg'[x] == ((1 + (3/4)*yb)^-1)*(-(3/4)*yb*n*vg[x] + (1/4)*k*dg[x]) +k*phi[x],
phi[xi] == 1,
dc[xi] == (3/4)*dg[xi],
vc[xi] == vg[xi],
dg[xi] == -2*phi[xi],
vg[xi] == -(1/4)*(k/n0)*dg[xi]},
{phi, dc, vc, dg, vg}, {x, xi, xrec}, {k}]
Plot[Evaluate[Table[phi[k][x] /. c, {k, 0.01, 1}]], {x, xi, xrec}]


When I run this code, the NDSolve part gives a parametric function, and it seems OK, but when I plot, I get the following error:

ParametricNDSolve::ndnum: Encountered non-numerical value for a derivative at x == 0.001.

What is the problem with my code? Is there anyway to fix it?

• I think your initial condition are bad. The reason the problem doesn't show up until you try to plot is because ParametricNDSolveValue doesn't do any solving, it just set things up for NDSolve to solve when a numerical value for the parameter has been given. Mar 30 '19 at 22:05

After correcting a couple of typos, the code works.

arec = 1/1100;
aeq = 1/(2.4*10^4*0.13);
alpha = (arec/aeq)^1/2;
y = (alpha*x)^2 + 2*alpha*x;
yb = y*(0.02/0.13);
yc = y*(0.11/0.13);
xi = 10^-3;
xrec = (((alpha^2 + 1)^1/2) - 1)/alpha;
n = 2*alpha*(alpha*x + 1)/((alpha*x)^2 + 2*alpha*x);
n0 = 2*alpha*(alpha*xi + 1)/((alpha*xi)^2 + 2*alpha*xi);

c = ParametricNDSolve[{phi'[
x] == -n*
phi[x] + ((3*n^2/2*
k)*(vg[x] (4/3 + y + yc) + vc[x]*yc)/(1 + y)),
dc'[x] == -k*vc[x] + 3*phi'[x], vc'[x] == -n*vc[x] + k*phi[x],
dg'[x] == -(3/4)*k*vg[x] + 4*phi'[x],
vg'[x] == ((1 + (3/4)*yb)^-1)*(-(3/4)*yb*n*vg[x] + (1/4)*k*dg[x]) +
k*phi[x], phi[xi] == 1, dc[xi] == (3/4)*dg[xi],
vc[xi] == vg[xi], dg[xi] == -2*phi[xi],
vg[xi] == -(1/4)*(k/n0)*dg[xi]}, {phi, dc, vc, dg, vg}, {x, xi,
xrec}, {k}];
Plot[Evaluate[Table[phi[k][x] /. c, {k, 0.01, 1, .3}]], {x, xi, xrec},
PlotLegends -> Automatic, AxesLabel -> {"x", "phi"}]
` 